If you have more than one television, cable box or cable modem that needs to be connected to the same cable signal, you must install a cable splitter. Splitters come in two, three or four-way configurations so that you can connect two, three or four items respectively to the same cable signal. Your cable company would probably be glad to install this for you, but since a cable splitter is inexpensive and easy to install, you may not even need to call them.
Identify where your cable signal comes from. Usually this looks like a light switch faceplate mounted low on the wall. Instead of a light switch, the end of a coaxial cable emerges from the faceplate. If you don't have a cable port installed already, you will need to have the cable company install one.
Choose which items need to be connected to the cable signal. These may include multiple TVs or cable modems. Verify that each unit has a place for you to connect the coaxial cable.
Connect one length of coaxial cable to the wall cable outlet. Connect the other end of the cable to one of the 4-way cable splitter's connectors; which one you use does not matter.
Install a coaxial cable to the appropriate connector on each unit that needs access to cable signal, then connect the other end of the cable to any free attachment point on the cable splitter.
Test the units to see if they're receiving sufficient cable signal. Splitting the signal may reduce its strength, so if the TV and/or cable modem don't receive sufficient signal to operate properly, you might need to ask your cable company to boost the signal or install a booster.
You can usually get coaxial cable for free from your cable provider.