Edit 12-9-2016: As of the most recent update, some parts of this guide are outdated. To change your mystic codes/costumes, it is now changed for each of your individual party slots at the bottom left. And in the options menu (sound settings and such) there is a button when you scroll down that when turned ON it will allow your friend list to view your servants using the ascensions that you use personally.
I purposely left out things that were generally covered in the tutorial like leveling servants and stuff.
Resources:
http://fate-go.cirnopedia.info/
http://fategrandorder.wikia.com/wiki/Fate/Grand_Order_Wikia
https://www.reddit.com/r/grandorder
Find me at:
http://www.twitch.tv/julinlin
https://www.reddit.com/user/julinlinlikespizza/
Tweets by julinlikespizza
https://discord.gg/XTtPjxH
Music used:
少女たちへのご説明 - Fate/kaleid liner Prisma Illya Season 1 OST