I don't have any sniper rifles, so I'm not sure if it would be different, but you generally just pull back the spring on the magazine, place the tip of the speed loader on or in the hole where you insert the pellets, and squeeze. And to the previous poster, don't say that paintball is better than airsoft, or vice versa. They both have their bonuses.
The UTG Master? Load up the speed loader, the catch on the back... Then press the button on the bottom side, that will relase the push-bar... Put the nozzle over the BB port on the mag, and depress the push-bar... Get it?? If you dont know how to use a speed loader, that's sad, sorry...