First time mom. Help with pumping

Abby

Hey all I am a first time mom my son is about 1.5 weeks old. Doctor told me to start pumping at 2 weeks to help build up my supply when I go back to work my question is when do I pump?? My son is eating every 3 hours..do u pump one breast while he eats off the other or pump both in between feedings?? I am so clueless about pumping and advice will help! Thanks in advance!