How do you inject dll files?

[Sloppierstorm84]

I've downloaded two injectors so far, namely:
-Valkyrie
-SDInject v2

I try injecting the files by adding or opening the dll file. Like, I open the injector, ass the dll hack like super pistol, and it says its injected. (I do this when A.V.A is opened, but not during gameplay). I wanted to know if I'm doing it all wrong. Or, should I add the injection during gameplay?I don't think there's anything wrong with my computer. It's a recently bought laptop which is Windows 7 64 bit.

Thank You So much!