Where the Hell do I Start

So, my mum kindly donated me her old Samsung Galaxy S, I just did a factory reset, but I don't really know what I should do with it as far as installing some new OS, or modding the ROM, or how to do all these extremely complicated  things on a phone.

Any tips and such would be greatly appreciated :)

well i guess my first question is do you need or want to install a new ROM on the phone?   there are plenty of sites that show you how to root it, just google how to root the phone and you'll see tons of tutorials on it. 

it's not complicated head over to XDA forum of Galaxy S check your model and read the how-tos it's fairly simple 

Yup, first you must need a reason ?

Just install a rom you think looks nice and then pick a launcher app.