You are right to be cautious about cutting...the suggestion of practicing on something like an old sheet is a great one...practice on that until you are comfortable with the cutter and rulers, folding fabric etc.
Another suggestion would be going into a quilt store and asking for a demo...or to take a beginner class.
I remember how scared I was of my rotary cutter when I first got it...back when they first came out....no one I knew had one to show me how to use it. It sat in a drawer for months until I finally got brave enough to take it out and try it. It is certainly a tool that has revolutionized the quilting world!