Here is a list of the most commonly repeatedly asked questions. These are almost all related to technical issues that people are having with the game.
Pokemon Go login issues after update
Is it possible to log back into a Pokemon Go account?
Does it make a CP difference if you feed candies before or after evolving?
Why are there no Pokémon near me?
I can't play Pokemon GO! What's wrong?
My Pokemon go account has reset
Forgot login credentials, can I look up my account from my username?