[how to] Add post formats ?

Hello world,
My current theme doesn't have "Format Post" templates, such as :
Gallery, Image, Video, Audio, Quote, Link, Status, Aside ... just have the "Standard"

And I'm wondering how complicated is this to add those options in my back office ?
Any specific page I can read to learn more about this ?
Or perhaps, there's a plugin who can help me achieve this ?
Thanks so much