How come sometimes i can only select vertices? I cannot select faces.
I was in O mode and using the Grab function.
Try to Right-click near the center of the face (where the fat dot is). I too had the same problems till I got this.
Good luck 
hmm You’re right…but sometimes there are no dots on the center of the face. I think I may be in the wrong “mode”?
Ctrl+Tab lets you switch between Face, Edge and Vers mode