vagcom for a noob ?

my knowledge of cars is nothing compared to a lot of users on this forum but ive got a few quick questions i hope someone could answer for me.

1) What does vag com actually allow you to do to a mk2 fabia? is it purely fault diagnostics or are there all kinds of funky features you can enable and change?

2) is it easy to use or are you likely to bust the car?

3) what do you need to to buy and is it expensive?

Ben