The sport messes with your head. The first time you have one of those little balls wiz by your head at about 300fps, you start thinking things. Your mind won't register that it's not going to kill you; it's telling you that hey that ball is moving pretty damn fast. Just to ponder how far that is lets do some math. 3feet = 1 yard, 100yards = 300feet, 100 yards is also the distance of a football field. So theoretically a paintball can travel the distance of a football field in one second. Now there are other factors involved in how they travel but I am not going to go into that right now. Let me tell you though the first time you get hit by one of these you will know it. It's a stinging sensation for about a minute but then it goes away. The only bad part is that you will remember that hit for about a week afterwards until that welt goes down.
The game is also physically tough; you have to run jump, crawl and sit, depending on what type of game you're playing. When I first started I was playing speed ball, took a run off the starting box and did a dive into a bunker. To this day I still have a chunk missing out of my thumb from where it slammed into the ground. Be prepared for anything. It's the closest I think humans get to war without being shot at with real bullets.
So you want to know how to get started? The first thing I can say is the sport isn't cheap. I have played with guys that spend thousands of dollars on their markers, AKA paintball gun, (due to BATFE Regulations they can't be called paintball guns, or else they fall under the National Firearms Act.)
What I suggest doing is going to a local field and see if they rent out equipment and try the game out. Remember the rental equipment is just that, a rental, they do this so new players (newbs) can try out the sport without going into a financial hole. Then if you want to continue playing, start buying your equipment.
There are four things that any new player has to have to get started and not get frustrated with the game. First, buy a decent marker. Don't buy the Wal-Mart $99 package deal. When it comes to markers you get what you pay for. Second, buy a good mask, not the cheap ones that fog up on you when you're playing. The worst thing is when your mask fogs up and you have 2 guys of the other team flanking you and now you're going to have welts on both sides of you. GET A GOOD MASK. You will also need a good air system. There have been a lot of debates on whether CO2, N20 or CA is best. Compressed Air is a bit expensive so for the beginner it is probably not the best choice.
Depending on the marker, some of them require either a CO2 regulator or using CA. C02 is a good way to start, make sure you get a large enough tank so your not refilling every game and don't leave the tank in the sun. When CO2 gets warm the pressure in the bottle rises and you will have your own miniature missile. (I know what you're thinking, don't try that at home). The last thing to get is if your going to play speedball, get a pod pack. They are small little backpacks that hold 2 to 8 pods of paintballs. Remember if you run out of paint in a game, you're a sitting duck.
Remember the most important thing in this game is SAFETY! Always wear your mask on the field, and if you're in an area that the barrel condoms come off your mask goes on. And of course... Have fun!