Main question is basically how do I know which one is active? I'm a complete newbie when it comes to these kind of things so any explanation would be appreciated.
If you want to know, integrated is Intel HD 4000, dedicated is Nvidia GT740M. Currently running on an ASUS laptop.
You should be able to set which card you want to use in the nvidia control panel. Right click on your desktop and select nvidia control panel. Should be in manage 3d settings or something like that. To make sure it is using the right GPU, you can download a program like EVGA precision and check your nvidia gpu usage while running a game. Should probably be something in the 90's unless your fps is capped.