Once you have the ISO, you need an emulator. The best option is PPSSPP, available on Windows, macOS, Linux, Android, and even iOS.
You might ask: why would anyone seek out a School Days HQ PSP ISO when the PC version is more accessible? Several reasons: school days hq psp iso
You have two options: play on original PSP hardware or use an emulator. Once you have the ISO, you need an emulator