One of my friends was going on about how he knew a guy who had a band ... who recorded a song using multitrack software on the pc and it turned out good, and then the band went and took the song they made on the PC and got it professionaly mastered or somn and it sounded a whole lot betta.

what is mastering? how do you do it without paying a heap of money? is it like intensive EQing of the entire song to get it sounding right or something?