If you cannot figure that out, maybe you should do some more researching, or another hobby. Not being a meenie, just sayin....... However, I will give you this, the best way to get air for the gun in the link you listed would be a shock pump!
Watch it!
Real moderator entered the room...
Actually it wasn't bad enough to start al this ranting.
Matty's right about doing some more research.( suggesting to him to take up another hobby
is kinda insulting...

)
You can't just link a newbie to a launcher and say: this is simple enough.
Do that.
Pedrojoca needs to learn a lot of things so it seems.
QEV....slide valve....T-mag... say what?!?!??!?!
Pneumatic launchers all share 3 basic components:
A barrel, a reservoir to hold the pressure and a valve inbetween to release that pressure.
You can learn about valves in the wiki.
I have made a pretty powerful mechanical launcher firing marbles with rubber bands and a system of pulleys.That could work.
But after you read through this forum and learn your basics you will still need tools to build it.
That goes for any type of launcher.
The simplest way to get multiple shots would be to use ballvalves.Basic turn-to-open valves.
use 1 reservoir or bottle to hold the bulk of the pressure.open the first valve and let pressure into your " firing" reservoir.Close the valve.
Open the second valve wich leads the air directly into the barrel.
This could be seen as an exercise to get into the world of pneumatic launchers.
You need to get the basics behind it,
After that you can learn about better and more sophisticated valves and learn about different loading mechanisms.
I don't think many of us started out with a multishot -ready to go to makebelieve war- kind of launcher.
Baby steps.All of them are fun...