How do you play online on your PS3

This depends on your internet connection and how your setup.

1) You will need Broadband.
2) If you connect to the internet through a router, connect the ethernet cable to ps3 and router, bingo, your done.
2a)If its wireless, you will need to tell your ps3 the wep/wpa access key, you will have had to do this with your PC.
3) If you connect through modem, you will need an ethernet port (nic card)on your PC, then enable internet sharing on that connection, connect the ethernet cable to both PC and ps3 and your online.

Ok here is an improved answer that happened to me in experience when i could of got ps3 online on Christmas but had NO IDEA what to do...
If u have a long enough ethernet cable then you take the ETHERNET cable out of the back of ur computer and plaug it into the back of your PS3 and make sure the ethernet cable is hooked into ur DSL MODEM, i think it might only work if u only use your internet provider, like AT&T for internet like for me, i have a MOTOROLA dsl modem, and take the Yellow ethernet cable out of the back of my computer and hook it up to my ps3 and then go to <Settings> find <Network Settings> at the bottom and then find <Internet Connection Settings> and then i think just TEST CONNECTION comes up and IP address should say SUCCEEDED and Internet Connection or something SUCCEEDED
then you can play online, there you go, hope it helps....