The first question that needs to be answered is: Are you legally allowed to buy a gun? Generally speaking, if you are over the age of 18 and NOT a convicted felon, you can purchase any kind of long gun (shotguns and rifles). If you are over the age of 21 and NOT a convicted felon, you can purchase both handguns and long guns. That's generally speaking. While not usually the case, there may be additional rules specific to your state. For example, some states don't allow anyone with a domestic violence conviction (even a misdemeanor) to own a gun. If you've never gotten in any kind of legal trouble, and you're over the age of 21, you're good to go.
The answer is surprisingly easy. Visit your local gun shop. Every gun shop is required to have an FFL or Federal Firearms License. This is a license issued by the BATFE (Bureau of Alcohol, Tobacco, Firearms, and Explosives), that permits a person or business to conduct the sale of guns. The rules about who can sell guns are pretty straightforward. If you are selling guns that aren't in your private collection, you're in the "business" of selling guns and you need an FFL. An FFL can legally transfer ownership of a gun from one party to another, and that's important if you're going to be buying a gun. Make friends with the folks at your local gun shop. They know the rules and regulations specific to the area that you're living, and they'll keep you out of trouble about what you can, or can't buy.
If you have a problem finding someone locally who is willing to do the transfer for your internet gun purchase, we can help. GunAuction.com has an FFL Network, a group of FFL holders throughout the U.S. who, for a modest fee, will do your transfer for you. Just search the FFL Network for an FFL holder that is nearby. Also, before you try to buy a gun online, it's a good idea to meet your local FFL holder in person and shake hands. You are after all, buying a gun! Before the seller ships a gun to that person, it's a good idea to meet the FFL holder in the flesh and introduce yourself. Let them know you'll be having someone send them a gun for the transfer. That'll also help avoid the uncomfortable surprise of the FFL holder having a strange gun arrive at their doorstep.
After you've found a local gun store willing to do the transfer, the next part is the fun part - finding and buying your gun online! Here at GunAuction.com, we have a huge variety of guns available for sale, from sellers all over the U.S. I can't tell you what kind of gun you need... Wait a minute... Yes, I can! You need them all. Buy them all. But don't try to buy them all at once. Make sure to save some for the rest of us and start slow by finding one gun you'd like to start with.
There are several attributes which recommend the 870 for self-defense work. First, it's the most common shotgun made in the world. There are tons of ammunition and accessories with which to trick out your new toy. Shotguns send clouds of lead in the bad guy's direction, and it's length means it's easier to keep pointed in the bad guy's direction. Your rounds are less likely to overpenetrate, which means that if you miss the bad guy, your rounds won't go through more than a few layers of sheet rock (a problem with larger handgun or rifle rounds). It's been made by Remington for decades, and will likely be made for decades more, which means plenty of spare parts. And it's a pump shotgun, which means the mechanism for loading your next shell is less likely to jam under stress. Lastly, in a pinch, it can double as a club. If you run out of shells and your home invader is still stupid enough to be around and upright, start beating him about the head until he's horizontal.
It's tough to do that with a handgun...