Order run down (off the top of my head)

Daughters of Khaine- murder elves there because slaneesh is chaos and they hate slaneesh

Idoneth Deepkin- soul stealing elves abandoned by daddy teclis

Lumineth- teclis's master elf race

Stormcast- sigmars douchebag elite

Sylvaneth- tree hugging hippies, elves and trees. Eco terrorists.

Fyreslayers- shirtless dwarves with axes

Kharadon Overlords- skyship greedy dwarves, steampunk persons wet midget dream

Cities of Sigmar- hodgepodge of races , lots of older models but people "reclaiming " things in the name of sigmar

Seraphon- memories of space lizards with memories of space dinosaurs following old space toads who willed them into existence to fight chaps.

Destruction

Orruks- you have violent green aboriginal men, violent green armored men, and sneaky green swamp violent men. Many pigs as mounts

Ogres- big bellied savages. Eat flesh. Hungry and avoiding the cold.

Gloomspite Gitz- psychedelic using goblins that ride spiders or wolves and dedicate life to the moon. Smelly trolls included.

Sons of Behemat- you want to field an army of 4 to 7 giants? Have at er...

Chaos

Slaves to Darkness- chaos undecided. Barbarian hordes . The I don't wanna commit to one chaos God fully army...of mortals

Legion of the First Prince- gimme all the demon flavors and let me summon demons.

Hedonites of Slaneesh- pain is pleasure. Chaos army dedicated to freaky stuff.

Disciples of Tzeentch- magic heavy. Let's follow big bird who cheats at dice and manipulates fate.

Blades of Khorne- kill maim kill maim die blood ....blood for the blood God. Shooting and magic aren't heavy here.

Maggotkin of Nurgle- flies diseases and pus. God of gross stuff. Tough army surprisingly killy.

Beasts of Chaos- evil chaos worshipping goatmen, minotaurs and other random beasts.

Skaven- warpstone fueled ratmen. Can nuke themselves as well as the enemy . Obsession with the number 13.

Death

Nighthaunt- ghosts. Ignore rend. Fly feed off terror. Not super hard hitting.

Soulblight Gravelords- vampires, zombies, wights and skeletons oh my! Several flavors of vampires. Awful tarpit unit to run up against.

Ossiarch Bone Reapers- Egyptian style dead. No command points . Other replacement effects. Doesn't play well with other Death armies( no allies)

Flesh Eater Courts- crazy cannibals that think they are nobles but really just eating corpses and the living. Ghouls and other malformed things