Go to your public library and check out their magazine section. The NRA magazine, The American Rifleman, is probably there and you can get an idea of what they do.
They're kind of like a flashaholics organization for guns, except that we don't have to worry that a large number of people and pretty much all the media seem to think flashlights (i.e. firearms to the NRA...) should be outlawed, banned, and possibly forcibly confiscated (despite a Constitutional amendment that sure sounds like it's a guaranteed right of free US citizens to have them). Living in California, I can attest that this conceern is not a paranoid delusion.
So, mostly good people who have paid dues to join an organization that supports firearms and the right to own them.