Most projectors are designed to be compatible with standard A/V connectors, meaning you can plug them in to a cable box or TV and allow the signal to be run through the projector. The easiest way to do this is with a VCR, DVR, or cable box that has video output ports. (Most newer TVs have video output ports as well, but if you get cable or satellite TV, you want to make sure the projector gets the signal from the equipment, rather than the TV.)
Turn off all of your equipment before you begin. You run the risk of shorting something out and possibly receiving a nasty electrical shock if you attempt this while one of the components is still on.
Check the back of your television, VCR, cable box, or satellite receiver. You should see a series of plugs labelled under the "Video Output" feature. The plugs will likely come in rows of three: one yellow, one red and one white. In some cases, you may see a circular black plug labelled "S-video." Connect the projector to any one of them.
Connect a set of analogue A/V cables into the appropriate colour-coded plugs on the back of the TV, VCR, cable box, or satellite receiver. For example, plug the yellow cable into the yellow plug, the red cable into the red plug and the white cable into the white plug. If you're using an S-video plug, simply plug it into the S-video outlet.
Connect the other end of the cables to the ports labelled "Composite" or "Input" on the back of your projector. The exact label may vary. However, the analogue A/V ports will be colour coded just like the ones on the back of the TV, while the S-video plug will be clearly labelled as such.
Turn on the projector and then turn on the TV, VCR, cable box or satellite box. The image should now be running through your projector, allowing you to watch TV on it.
Many projectors have small and rather tiny sound systems. If you have a stereo system or speakers which you currently use for your TV audio, you can still use them without difficulty. Simply refrain from connecting the red and white cables in your A/V cable set. Connect the yellow cable or S-video cable as normal. That will send the video signal to the projector, but not the audio signal, allowing you to project the image without sacrificing sound quality. The central question in connecting your TV to your projector is which component to connect to the projector. If you only have a TV, without a cable box, satellite box or VCR, then connect the projector to the TV. If you have a VCR and primarily watch your shows through it (i.e., you have to turn your VCR on to watch TV), connect the projector to it. Otherwise, connect your projector to your cable or satellite box. DVD players and Blu-ray players do not normally receive television signals (instead, they send the signals from the disc they are playing to the TV), and thus are not normally involved in an operation such as this.