I periodically get the question about using a foam roller for back muscles. The foam roller works incredibly well for a lot of different muscle groups, but the back can be a challenge. In researching something for a client, I ran across this website with some really helpful information on how to do it.
Remember with foam rolling, or actually with any self-massage tool, it usually takes some practice to get it right. Learning how to position yourself, how to use the right amount of pressure, etc. may be challenging in the beginning. But, stick with it. The more you care for yourself between sessions, the better you will feel!