What are paintballs? Well, they are small gelatin capsules filled with a water-soluble marking dye. The dye in the capsule in not toxic, which means that it won't hurt you even if you were to gulp it down. But, I wouldn't ingest it if I were you, that is unless I liked the taste of ink!
Many different companies supply paintballs, ranging from expensive tournament balls to much cheaper bals of lower quality of recreation. If you have a look at www.sakworldpaintball.com you will see some of the ones available. They come in pretty well every color and quantity.
In general, paintball fields require you to buy your paint there, because this is how they make money. However, many fields nowadays allow BYOB (Bring Your Own Paintballs) for a small fee.
The kind of paintballs you will be purchasing for yourself will depend on how you intend to use it. Some have a thicker fill, some have a thinner fill. Take a look at http://www.sakworldpaintball.com/paintballs.html for different types of paintballs.
For practical purposes, you are more likely to go for a cheaper product, and quality might not be a top priority. Of course, a tournament ball will need to be the best, and you have to have balls that won't burst in your paintball gun. On the other hand, you need bals that will easily smash into your opponents.
Apart from its quality the other important factors you must pay attention to is the size of the paintball. Your paintballs should fit into your paintball guns perfectly. Paintball sizes are measured in calibers. Paintballs are all .68 buts its the last number that makes a difference. Most paintballs these days are .689. If your local field paint is too big for your barrel you might consider getting a new barrel http://www.sakworldpaintball.com/paintball-barrels.html .
Usually, most paint gun barrels are of .68 calibers. But knowing the exact measure of your paint guns barrel is a pre-requisite for all paintball purchasers. If your ball doesn't fit into your barrel your shell will break and none of the balls will leave your paintball gun in one piece.
Paintball guns themselves come in a number of varieties, like the paintballs themselves. Consider the Ion gun, which has all the standard features you woudl expect, plus is extremely versatile. Think about your level of skill and expertise when choosing a gun, as well as your budget. There's no point having an excellent gun if you can't aim it accurately. If you have a look at http://www.sakworldpaintball.com/paintball-guns-markers.html you will see a list of paintball guns you might be interested in.
Take another look at the Ion gun. It has a 17/sec fire rate, and an automatic fire rate of 10 balls/sec. This alone makes it worthy of consideration, but its price is so low that it could be used for recreational play as well as tournament. So go to http://www.sakworldpaintball.com/smpaionpagun.html and have a look.
If you want a top end paintball gun, then have a look at Planet Eclipse (http://www.sakworldpaintball.com/planeteclipse.html). Planet Eclipse makes guns which shoot over 30 balls/sec, and are some of the best available.
But if you don't know what exactly you want, have a look at SAK WORLD PAINTBALL (http://www.sakworldpaintball.com). They are one of the best online stores, and keep up to date with the newest guns.