All air soft guns have a fps (feet per second) that determines how fast they shot. A good gun should have a fps anywhere from 335-500 fps. Very rarely you might find a gun that has 615 fps. (that's the highest I've seen without any upgrades)
I have many guns, my favorite gun that i have is my is a Panther Carbine.It started of with about 375 or 385 fps. Now it has around 500 fps. How did i make it gain so much fps. the answer is MODIFICATIONS. i added a new spring, barrel, and wind resistance. I also added a laser, laser scope, and to neon flashlights.
Once you have bought your air soft gun. You haven't really have the full experience till you have an air soft WAR! Get a gang of your friends and pick teams. It's a ton of fun and helps teach leadership. Make sure the teams are fair. Its no fun for the unfair team who just keeps losing. For example, ten friends and six have pistols, the other four have rifles, and all the rifles are on the same team. That's not much fun for the people with the pistols. So spread it out evenly!
One more word of advice, get your air soft gun from a legit place. Like Big 5, or any other air soft dealing store. ( not a grocery store)