If you are 18years or older, you can purchase a rifle or shotgun without a permit. Just fill out the paperwork that the gun store has you fill out, have ID and proof of residence, and wait the 10 days... simple as that.
If you want a pistol, you have to get a handgun safety certificate and be 21 years old. Any gunstore will sell you one. You have to take a lame ass test that any 8th grader could pass (common sense), pay the $30 or whatever, and then you get your cert. Buy the gun, fill out paper work, wait 10 days, and you're done.
If you buy a gun online, it needs to be sent to your local FFL dealer (local gun shop) before you can have it).