downgrading my psp so it can play free games?

i have been hearing that you can download free games for your psp but i also heard that to do this you have to downgrade your psp. i found a site that tells me how to downgrade and even has a free download of the files(pandora battery files) to make this happen http://forums.digitaltrends.com/showthread.php?t=13122 but my problem is thatat the bottom of the page it says that the process is irreversible and that you wont be able to use your psp normally of something??? i have also been reading that you can put custom firmware on your psp what is this??
why does everyone have to make this so confusing can someone please tell me everything i need to know about downgrading my psp saving games onto it saving emulators on it and saving games that you can play on these emulators.
can someone who has just done all of this themselves please give me all the info i need and it would be much appreciated and maximum points will be given to you
so please help!!!!