I want to play simple games like diablo 3 or sims and Internet stuff also work stuff on a laptop and don't know the difference between intigrated graphics and the dedicated graphics. I want a MacBook Pro do I need to get one with the graphics card or will I be ok without one? I can spend the $2500 if I have to but would like the cheaper one if possible.
You can check the hardware requirements of the games you want to play in the App Store. This will give you a good idea on what exactly you'll need.
If you look at the latest machines, you've got the built-in Intel Iris 6100 graphics with optional AMD Radeon R9 M370x.
If you're concerned about gaming, the AMD chip is going to get you roughly 20% faster performance and slightly better quality lighting than the Iris can do.
One nice but probably less important thing to note is that the AMD chip has its own dedicated video memory (2 or 3GB I think) whereas the Iris chip steals from your main RAM pool as needed. GDDR5 is faster than DDR3/DDR4 (or whatever is in the MBP), but that probably accounts for a few percentage of the speed increase.
The AMD chip is only switched on when needed, so under typical desktop mode you're going to be running the Iris. However, the AMD chip does allow for a 4K display to be connected via the Thunderbolt port at up to 5120x2880 which the Iris alone doesn't support and thus would enable the AMD chip for desktop.
So it comes down to getting the separate GPU if you want slightly better gaming or ability to use a huge external display.