Go to that site on your computer. Pick what you want. Set your phone choice.
I typed virgin and saw many models of Motorla but not my model. I typed Kyocera and saw many models there, but again not mine. I'm guessing my model does not do apps. I picked one anyway. I then clicked download. It prompted me to go to the phone and browse to a particular website (short typing). Then I could enter a 5 digit code it gave and expect the download to start.
I suspect the phrase "jar" in web site name implies that they are all java code. If your phone supports java (most likely if it has a browser). It wont matter about the OS, you'll be good. Try something small and simple first.