Since someone asked how to see the meta and subtags, let's look at an example:
An Archive of Our Own, a project of the Organization for Transformative Works
This is what we call the tag landing page. You can reach it when you're in the tag by clicking the link at the top of the page, e.g. where it says
1 - 20 of 1,885 Works in Centaurs
the underlined 'Centaurs' is a link to that tag's page.
The first thing you see is the Parent tags. This is, in general, what fandom a tag is stored in. For a tag like Centaurs, which can apply to many different fandoms, that is "No Fandom".
Then we see "Tags with the same meaning". These are synonyms/syns of the tag in question. If you tag your work with "she's a centaur", it will be made a synonym of Centaurs and appear under that tag.
Then there are Metatags. In this case, Mythical Beings & Creatures. A centaur is a type of mythical being, so it's a subtag of that tag.
Then there are Subtags. These are tags that are more specific - mostly specific characters as centaurs, in this case. If you choose to exclude the Centaurs tag from your search, you'll also be excluding Centaur Castiel automatically.
All of these are links - you can use them to navigate up and down the tree, so to speak, for instance if you want to see what other mythical beings and creatures are included under "mythical beings and creatures," you can click on that to go to that tag's landing page.