How do I know if I should send AP scores to colleges??

In general, most colleges will only give credit for 4s or 5s, so see if your college gives credit.  Then consider if being in the the more advanced class will be ok for you in terms of challenge, because you want to protect your GPA at all costs.
 
If you decide you want to send AP scores to your college, then you do that through the CollegeBoard website, in June or July after Senior year, when the scores become available.
 
Hope this helps!
Yay, college!
Susanna