How to actually start meditating

   Hi guys. As I'm sure a lot of other people here are I am an anxiety and ocd sufferer. It's kinda controlling my life and while I'm generally happy I always end the day exhausted and in pain because I'm just so tense all the time. My dad (who also deals with anxiety) and psychiatrist recommended mediation to help me center myself and clear my head throughout the day. 

   I guess my question is: How do I actually do it?? Do I just sit and breath? Are there any mental exercises I have to do? Mantras? Breathing?? Pose???

What advice do you have for a bare bones beginner and how did you personally start meditating, technique wise?