Like almost all emulators, you'll have to download the BIOS yourself. This is very important, because if you don't get a BIOS, you won't be able to play anything, no matter how many ISOs you have on your device.
The free version of DamonPS2 a few obvious differences when compared to the paid version, the most noticeable being that the free version has ads. The free version also doesn't allow you to save to a memory card (although you can save from the emulator itself), and has fewer graphic options. Even so, tons of PS2 Games run perfectly on the free version.
Play legendary PlayStation 2 games like Metal Gear Solid 2, Silent Hill 2, Final Fantasy X, God of War, Onimusha, Disgaea, and many more on your Android device with the full featured emulator DamonPS2.