Everyone has given you excellent advice. I'd like to throw in my $0.02.
When you begin to study the rulebook, LEARN THE DEFINITIONS. I was told this my first year, and I THOUGHT I knew the definitions because I watched the NFL and College ball. Don't rely upon any presumed knowledge of the definitions. These are the keys to understanding the rest of the rules and the announcers defintions can vary greatly from the rulebook definitions.
After understanding and learning the definitions, then learn the football fundamentals listed in the back of the rulebook.
Once you have a good understanding of these items, you will be well on your way to grasping the rest of the rules.
And finally, keep posting here. This is an OUTSTANDING place to learn and ask questions.
Good luck!