Well, I quote
@sakindia123 here, as this is generally attributed to him:
Yes, it really is that simple. Just look up some guides, try to get them sources synced first... Do some prebuilt builds first, no changes. Then, start playing around with device tree and stuff... And, most importantly, try to solve them questions you get by using your friend Google, they made android, they can't get better at getting you to places where you can get "documentation" for it