Well why not? I don't know what it really is but if it's explained I'm sure I can get it. I finally learned this year how to count pass four so there's hope.
Each person in the league has their own team. At the start of the season (a few weeks before NFL football actually starts), a draft takes place. The draft time is set up in advance by the league, so all (or most) members can log in and attend the draft. A draft order is picked at random, and each team takes turns filling out their roster from the actual NFL roster. All active NFL players are draft-able. If you can't be there for the draft, you can "pre-rank" your players--who you want most, in order, based on availability. Your team will be drafted for you based on this list.
Now, as for actual play. Each week, as NFL games are played, each player's stats for the week are totaled, and give you a certain number of points based on that performance (specifics differ between leagues). Team with the most points wins. There are different styles of leagues, (head-to-head and rotisserie come to mind), and the rules differ. I prefer head-to-head, myself, where you are up against a specific team each week. In rotisserie, you are always competing against the entire league (I'm in a fantasy baseball league like that now, and the standings change every day).
The fun is really in dealing with other owners. Drafting, trading, replacing injured players, getting guys off the free agent/waivers list, etc. It's a lot of fun, but requires a certain amount of upkeep.