There are many different types of magazines (clips) you can use to fit your style of airsoft. There are standard capacity, Mid capacity, high capacity, and box/drum magazines. Standard capacity magazines hold the amount of bbs that the real gun replicated can hold. You have to load this style magazine with some sort of speed loader. An example is a real ar15 style rifle holds 30 rounds. The advantage here is you can play more realistically and bbs don't rattle in side but the down fall is you have a small amount of bbs. So the standard cap magazine for the airsoft ar15 style rifles hold 30 rounds. A mid capacity magazine holds more than a standard cap but less then a high cap. You also have to load mid cap mags with a speed loader. Mid caps are becoming more common because you change mags more often but not every trigger burst. Advantage is your bbs don't rattle and you get to change mags frequently. Disadvantage you have about half of the rounds of a average high capacity magazine. High capacity is probably the most common due to its size and ability to hold a couple hundred bbs. These also usually come standard with your airsoft gun. The advantage is you get to hold a large amount of bbs in a normal size magazine. Disadvantage is you don't change mags causing you to lose realism and the bbs rattle when you move. You also have to constantly wind up your magazine. High capacity magazines are loaded into a compartment and there is a winding wheel you have to turn to move the bbs from the compartment into where it loads up into the gun. Box/drum magazines hold a 1000 to a few 1000 rounds. They sometimes automatically wind them selves up electronically with a sensor. Advantage is you Wont run out of ammo. Disadvantage is you have to use batteries or wind constantly and you will never change your mag. I personally use 75round or 120 round mid caps but when i am feeling lazy i use my lonax high caps which i will do a review on. Now that i gave you a run down on the basic types of mags maybe you will find it easier deciding on what to use.