You need an HDMI cable (not included with PS3)
Then if your TV isn't a piece of **** it will adjust automatically.
You can also adjust in your TV menu and PS3 display settings.
Note: Not all games and such will play in the highest available HD your TV can perform at.How do i change my Playstation 3 Display settings to make it fit to my television?
HDMI is the only thing that supports 1080p, so if you are trying to set it for 1080p it wont work as you dont have the HDMI cables. Change your video settings to a lower resolution setting such as 720 or 1080i until you can get some HDMI cables.