You need to have your PSP games as .CSO or .ISO files. I do not have the right to distribute those, so you'll have to get them on your own. The best way is to convert your real PSP games. To do this, you need to install "Custom Firmware" on your PSP. Google for that. Then follow these steps:
There are tools to turn ISO files into CSO (compressed ISO) files to save space.
If you have digital downloads on your real PSP, they can be used directly on PPSSPP. Just copy the EBOOT.PBP over. Note that this has not been tested as much as ISO loading so there may still be issues with some games.
You need a jailbroken iOS device, running iOS 6 up to 10.x. See the Downloads page for more info. Note that the JIT does not currently function on 64-bit iOS builds - this will be fixed in the future though.
To emulate advanced systems like the PSP fast, the emulator needs to translate the machine code language of the PSP to the machine code language of your PC or mobile device at runtime. This is done with a "Just-In-Time recompiler" or JIT, also known as a Dynarec. PPSSPP has JITs for x86 and ARM, 32-bit and 64-bit.
For a JIT to function, an app needs to have the ability to generate machine code at runtime. This is allowed on Windows, Mac, Linux and Android, while it is completely disallowed on non-jailbroken iOS and on App Store Mac apps, and on Windows Phone 8. It's possible on Windows Phone 10 but it has a deficiency making it very unreliable on ARM.
Install it exactly the same way as you would on a PSP, that is, copy the files to PSP/GAME or PSP/SAVEDATA (depending on the DLC) on the memory stick. In the Android version of PPSSPP, the memory stick is simply the SD card or USB storage of your phone, PPSSPP will create a PSP folder in the root of that. On Windows without installer, the memory stick is the "memstick" subdirectory in the PPSSPP folder. On iOS, it's in /User/Documents/PSP/ . On Mac and Linux, it's in ~/.config/PPSSPP.
No. PSP Vita is a completely different machine, far more powerful than the PSP and with different security technologies. I don't have neither the information needed nor the time.
No. PPSSPP simulates the BIOS (not really a BIOS on the PSP, more like an internal OS).
You're probably a Windows user. Because x86 CPUs are damn fast, PC GPU drivers are good, we have a fairly advanced x86 JIT, it's written in C++ and I rock.
You probably run PPSSPP on a mobile device. These devices, especially older ones, often have very poor OpenGL ES drivers, although the situation is improving. Some newer devices now have Vulkan support, which helps. The CPU emulation through JIT is now fast enough that it usually is not the bottleneck.
Why not? The domain name ppsspp.org was available.
Unfortunately there is no way to get information about Android app purchases, so I can't pre-approve email addresses or something like that. But feel free to use the free PC version indefinitely.
Yes, PPSSPP has built-in XInput and DirectInput support on Windows so it will "just work" with any Xbox 360 pad and most other pads that you plug into your PC.
On Android, many gamepads like Ouya's pad or Moga work just fine, sometimes with a few limitations. One remaining problem is that the Xperia Play buttons will work but not the touch sticks, for technical reasons.
Any reasonably modern CPU will be just fine, and any GPU that can handle OpenGL 2.0 should have no issues. You should make sure to install the latest graphics drivers available though. Windows XP or later is required, Windows 7 or 8 is recommended. Vulkan can help performance where available, also try D3D9 or D3D11 if OpenGL is slow by changing the backend in settings. On some older computers, you may need to use the DirectX backend.
CSO are compressed ISO files that can be played directly, decompressing on the fly. Very useful to save space on your Android device, for example. MaxCSO is a great program to create CSO files. Of course, there are others around the web, too.
You can either help out with fixing it, or wait until someone does.