Birth control

This may be a completely dumb series of questions, but I am new to the realm of Birth Control. 
1. What is the best type of birth control PILL? 
2. Does it alter your periods? If so - how do you know if you have missed a period and need to take a pregnancy test? I know BC is supposed to prevent pregnancy, but there's always a chance and I am overly paranoid and cautious. 
3. What are the most common side effects?