HELP!!!

Hello....I was instructed to download an e-Book for my English 102 class. Everything was going okay until it asked me to find an app to open the book that would accept .acsm files. I have no idea what that means. When I thought I had figured it out it asked for a code. I didn't buy the book myself....it was given to me by my instructor. What do I need to do?!? If you need more info to help, please just ask.

Thanks,

Bethany