Do I have to craft a badge?
Yes, you have to craft a badge.
Before I was level 10 cards gave me XP, why don't they give me XP anymore?
You never get XP from only cards, you get XP from crafting badges and buying games (2-3 xp per game) and some special badges such as "X+ games owned" or "member for Y years".
How much XP will I get from crafting a badge and leveling that badge up?
100XP, for initial crafting and each leveling up.
You can level up normal badges until it reaches level 5, but foil ones have only one level. Foil badges give 100XP too.
The amount of badges required per level is
floor(level/10)+1, so lets say that you are level 15, it is
2 because the amount of XP required to level up increases by 100xp on every 10 levels.