title_body: Portafilter difficult to turn
upvoted_answer: As your question is very open I will try to answer two common roots of your problem.
  
  1) Too much coffee. Per cup of espresso it should be 7g of ground beans.
  
  2) No "tamping". You probably did not compress the powder in the porta filter (called tamping). This is what it looks like:
  
  
  
  So maybe you compressed it when you tried to place it in the machine.