I grew up watching football with my dad and enjoyed football more than my two brothers. (By the way, I am a big Chicago Bears fan.) I started dating my now-husband during baseball season (I'm not a big fan but who doesn't love the Cubbies?) but it was during football season that he fell in love with me. I think it was the time that I yelled "Come on! My grandma can tackle better than that!" or maybe it was when I screamed "What the hell, no flag?! That was pass interference!" He'll tell you it was when he realized that I actually know what a bootleg is (it isn't a reference to the shape of Italy), I can identify a shotgun formation and point out when it would be a good time to go for it on 4th down. Most of all, I think he likes the fact that other guys are impressed by my football knowledge.
I'm not suggesting that you single ladies out there learn football to get a man. Although there are those who recommend it. I agree with this woman that it's better for single girls to look for men at sports bars than at night clubs. For my money, I'd much rather be eating spicy wings and watching football than drinking overpriced alcohol and trashing my hearing with crappy techno music. But I don't agree with her assertion that men who can commit to a favorite sports team can commit to a woman. There are plenty of men who have no problem sticking with their team but who couldn't commit to a woman to save their lives.
I'm simply saying that you can really impress men, if you're so inclined, by knowing your football. So, to help you in that endeavor, here are a few websites and books to get you started. The most comprehensive website is probably this about.com article. It really covers the basics and is good if you know nothing about football. There are others but most of them that are geared towards women are rather sexist or just too basic. You aren't going to impress anyone after reading those articles.
As far as books go, there's the usual "for Dummies"
One of my favorite football books is this one:
It won't really teach you about the game. But you'll get a good laugh and maybe be a better spectator. Making a few of the recipes might be impressive, too.
*Totally unrelated aside here - the best in the series that I've read is The Complete Idiot's Guide to Middle East Conflict, 3rd Edition (The Complete Idiot's Guide)