What sort of connectors do you have on the computer and on the TV? Some newer TVs have ports built-in that are compatible with the common computer output ports:
1. VGA Port
2. DVI Port
3. Composite Video Port
4. S-Video Port
5. HDMI Port
6. Component Video Port
If your computer and your TV have any of those ports in common, then all you need is a cable to connect them. Otherwise, you'll need a converter which are usually pretty cheap.
A word of warning: if you're planning on connecting an older CRT TV to a computer you should bear in mind that CRT TVs have very low resolution compared to computer monitors. SO so that it's near-impossible to read normal-sized text on them.