Wicca is a NeoPagan religion that can be traced back to the Witchcraft Revival of the mid 20th century. Gerald Gardner is considered to be the forefather of the religion, having made it public in the 1950s, albeit it existed prior, as Gerald Gardner himself was initiated into the New Forest Coven by a woman known as Dafo, aka Edith Woodford Grimes.
I myself follow NeoWicca, which will have more detail below.. As such, any information in regards to Traditional Wicca take with a Grain of Salt as I am not initiated into one of the many traditions of that category.
Wicca follows a duotheistic framework, worshipping a Goddess of the Moon and Earth who is generally seen as a giver of all life, and a Horned God, often associated with the Sun, who is a god of death, hunting, and resurrection/rebirth. These two deities are seen as a divine couple, whose union is the fertility of all things (the land, animals, etc. ) and the source of all creation. These two deities often are seen as two halves of a greater universal divinity.
This does engage with a cis-heteronormative framework, however, all life is generally born from a union of that sort. This does not mean Wicca is inherently transphobic or homophobic. That is simply the union of our gods, and they discriminate against none, as they are two polar ends of a vast spectrum, and even then, The Goddess herself has many emanations that are known for having genderqueer, transgender, and gender-nonconforming clergy.
If the idea of the gods engaging with concepts of gender and having roles that can be considered gender based makes you uncomfortable, that is fine, it just means Wicca is not right for you. Just because a tradition is not right for you does not make it bad or less valid than other traditions.
The union of the Goddess and God are documented through a mythological cycle that is portrayed through the Wheel of the Year. Their union and myth cycle is then reflected in the seasonal changes of the landscape.
How one approaches the theology of the gods will vary based on the practitioner and their tradition. Some may view the gods as tutelary deities in a sea of many, others may view the Great Goddess and Horned God as the primary deities of which all gods & goddesses are emanations of, and others may hold both of those stances to be true, as Wicca is Orthpraxic, not Orthodoxic. There is no right or wrong way to believe in the gods, but our practice revolves around these specific deities, whether your approach is soft or hard Polytheistic.
In most forms of Traditional Wicca, ESPECIALLY BRITISH TRADITIONAL WICCA, the names of the Goddess and God are oathbound, and only revealed to initiates. This is part of experiencing the mysteries of the religion.
The names of the gods may vary from tradition to tradition, and that is fine. This is why many see the specific names gods as tutelary deities of a tradition. For example, one tradition may use the names Ashtoreth and Tammuz for the Goddess and God, and another may use Diana and Pan. This does not mean one tradition is wrong and the other right, this simply means those godforms are the ones honored in that tradition.
Of course, other traditions from the Mid 20th Century Witchcraft Revival worship these deific archetypes & gods, albeit with a different approach. Just because a tradition worships a Moon Goddess and Horned God doesn't make it Wicca by default, but it DOES make it tied to the Witchcraft Revival if that makes sense.
Wicca comes in Two forms: Traditional and Neo.
Traditional Wicca is initiatory, and more often than not, Oathbound, meaning it is what we would call today, a closed practice/religion. You CANNOT practice Traditional Wicca without an initiation into the tradition. In regards to Traditional Wicca, there is British Traditional Wicca, which explicitly can trace its lineage back to Gerald Gardner and/or the New Forest Coven. If a Tradition claiming to be British Traditional Wicca cannot trace its lineage back to the New Forest Coven, it is not British Traditional Wicca. (The exception to this may be the Horsa Tradition founded by Sybil Leek, but I am not a BTW initiate so I cannot say for certainty if lineages back to her count as BTW.)
There are MANY traditions under the Traditional Wicca umbrella. Some BTW Traditions are Gardnerian, Alexandrian, Central Valley Wicca, AlGard, New York Wica, and Blue Star Wicca (I may be wrong about Blue Star and New York trads, so take that with a grain of salt).
Some traditions that are NOT BTW come to mind are the Georgian tradition, Seax-Wica, McFarland Dianic (NOT to be confused with the Dianic Wicca of Z. Budapest, which is rife with Terf Ideology and transphobia. McFarland Dianic is inclusive from what I've heard), and Odyssean Wicca.
As mentioned above the Horsa Tradition is in a weird spot in regards to whether or not it's considered BTW, as it formed around the same timeframe as Gardner's craft, and stems from a similar region in England. (If any Horsa initiates or BTW initiates could inform me on the status of Horsa's classification, please do!).
You CANNOT be a traditional Wiccan without initiation.
NeoWicca refers to the forms of Wicca that are generally not tied to any specific tradition, and based upon the works of authors such as Scott Cunningham, Raymond Buckland, Silver Ravenwolf, etc. NeoWicca, unlike Traditional Wicca, is not always initiatory, though there can be NeoWiccan Traditions that do have an initiatory structure and may or may not be oathbound, so definitions really can be kind of blurry at times. Generally though, I differentiate NeoWicca vs Traditional Wicca traditions based on when they were formed, how they formed, etc.
One could argue that any Non-BTW trad would be NeoWicca, though I feel that would lack a much needed nuance, as there are many traditions of Wicca not tied to Gardner that are just as rich in history.
The information you see about practicing Wicca in "Wicca 101" books will be NeoWiccan, as by and large the materials of Traditional Wicca are kept secret. I consider pretty much any practice outside of Traditional Wicca to be NeoWicca.
NeoWicca often overlaps with Eclecticism and has been called Eclectic Wicca, albeit I personally differentiate the two, as much of what is considered Eclectic Wicca today does away with what makes Wicca, Wicca.
So What Makes Wicca, Wicca? To me, the practices revolving around the veneration of the Goddess and Horned God, and the Wheel of the Year, are what makes Wicca, Wicca. Without the core theology of Wicca, we would not have the practices of Wicca, the Sabbats(the holidays), Esbats, etc. Without the gods, without the wheel of the year, it's not Wicca, it's simply Eclectic Witchcraft. You wouldn't take the Theoi out of Hellenismos, You wouldn't take the Neterju out of Kemeticism, so don't remove the Moon Goddess and Horned God from Wicca.
So You Want To Be a Wiccan, Now What? Research, do deep dives into the history of Wicca, Read Books, etc. Figure out whether or not you want to pursue initiation into a Traditional Coven, or if you want to practice NeoWicca (as a solitary or even in a coven). There's plenty of wonderful resources out there, and plenty of downright shitty ones too. Avoid Tiktok like the plague, as it's ripe with misinformation. Most social media treats witchcraft like a trend and pop-spirituality, it's not.
Materials To Get You Started:
Modern Wicca - Michael Howard (my go to reccomendation for a deep dive into the history of Wicca)
Buckland's Complete Book of Witchcraft - Raymond Buckland
Living Wicca - Scott Cunningham
Witchcraft For Tomorrow - Doreen Valiente
Lid Off The Cauldron - Patricia Crowther
A Witches' Bible - Janet & Stewart Farrar
The Witches' Goddess - Janet & Stewart Farrar
The Witches' God - Janet & Stewart Farrar
Traditional Wicca - Thorn Mooney
The Craft - Dorothy Morrison
Rebirth of Witchcraft - Doreen Valiente
Wiccan Beliefs and Practices - Gary Cantrell
@essence-of-wicca and @sova-witch (run by my lovely mutual!!)
(quick edit bc disclaimer: this is a little bit rushed as Im writing this on the clock at my job. Edits and revisions will likely be made)