What exactly are you looking to do with your system?
You might want to take a glance at our tutorials section, and if you know what you want but arent quite sure where, how, or what to do then you could take advantage of our help section.
There just too many things to list, but i can list some of the most common basic features...
Custom firmware: These are firmwares developed by homebrew coders made to combine 1.50 firmware as well as the latest firmware into one package enabling the use of homebrew on the latest firmware.
Emulators: These are programs you can throw on your psp to emulate another system (NES, SNES, Sega Genesis, etc.)
ISO/CSO: These are psp games loadable from a memory stick.