[No image this time because I didn't want to poorly edit the primary three types together.]
Elemental Daedra, better known as Atronachs, are a subtype of Daedra that are highly intelligent and show little to no kinship or loyalty to any Daedric Prince.
The most well-known subtypes are Flame, Frost, and Storm; other variants include Air Atronachs, Ash Guardians, Fire Daedra, Frost Daedra, Iron Atronachs, Shadow Atronachs, and Stone Atronachs. There are minor types, but these don't have much lore to them. For the purpose of this post, we'll be focusing on the three most well-known ones.
Flame Atronachs are native to Infernace and are considered the weakest of the three primary types. They often levitate (which allows them to go over water safely), are immune to Fire and Poison damage (in Oblivion), and are weak to Frost damage (in Oblivion). They have a hatred for Frost Atronachs but can put this aside when serving a mutual master. They are a source of Fire Salts.
Frost Atronachs are native to an unnamed part of Oblivion. They can breathe underwater (in Skyrim), can self-heal (in Oblivion), are immune to Frost and Poison damage (in Oblivion), and are weak to Fire damage (in Oblivion). The hatred of Flame to Frost Atronachs is shared in the reverse, with the same caveat to put it aside. Their names often begin with "Nomeg". They are a source of Frost Salts.
Storm Atronachs are native to Levinace and are considered the strongest of the three primary types. They are largely unorganized and chaotic and are found in many Daedric realms. They can levitate like Flame Atronachs (thus can go over water safely), are immune to Shock, Poison, and Paralysis (all in Oblivion), and have a lot of health and little that they're weak to. They are a source of Void Salts.
It has been proposed by @mothmaam that you can summon an Atronach as a familiar and provides a spell to do so (linked in the sources). Following this idea, you could also shape thoughtforms or servitors to look and work like Atronachs do.
You could also call upon them as experts in their field of magic - fire and heat-based spells for Flame Atronachs, cold-, frost-, and ice-based spells for Frost Atronachs, and lightning-, storm-, or thunder-based spells for Storm Atronachs. These spells don't have to be baneful magic, but these would best fit if you were casting spells associated with the Destruction school of magic. This includes all forms of baneful magic, energy work, protection, shadow work, sigils, wards, and weather magic (Flame for sun, Frost for snow, and Storm for rain).
https://en.uesp.net/wiki/Lore:Elemental_Daedra
https://en.uesp.net/wiki/Lore:Flame_Atronach
https://en.uesp.net/wiki/Lore:Frost_Atronach
https://en.uesp.net/wiki/Lore:Storm_Atronach
https://en.uesp.net/wiki/Oblivion:Daedra#Flame_Atronachs
https://en.uesp.net/wiki/Oblivion:Daedra#Frost_Atronachs
https://en.uesp.net/wiki/Oblivion:Daedra#Storm_Atronachs
https://en.uesp.net/wiki/Skyrim:Daedra#Flame_Atronach
https://en.uesp.net/wiki/Skyrim:Daedra#Frost_Atronach
https://en.uesp.net/wiki/Skyrim:Daedra#Storm_Atronach
https://the-college-of-whispers.tumblr.com/post/661947710698668032/conjuring-an-atronach
https://the-college-of-whispers.tumblr.com/post/662038308530044928/fire-salts
https://the-college-of-whispers.tumblr.com/post/662038308519591936/frost-salts
https://the-college-of-whispers.tumblr.com/post/662038282975297536/void-salts
https://the-college-of-whispers.tumblr.com/post/656421223701626880/magic-arts-oblivion
https://the-college-of-whispers.tumblr.com/post/656149429878980608/magical-skills-skyrim