Summarize this article in one sentence.
While rare, some modems encounter issues when paired with a specific Internet company (e.g., Comcast). Double-check your modem's compatibility with your current Internet subscription before buying (if possible). If you find that your modem won't work with your current subscription, try to exchange the modem for a different one that will work, or switch your Internet subscription. The cable output resembles a metal cylinder with a small hole in the middle and screw threads all around the sides. You'll usually find cable outputs in the wall near the floor in living rooms and bedrooms. In some cases, there will already be a cable connected to the cable outlet. The modem should be relatively high up (e.g., on top of a bookshelf), and it will need to be close enough to the cable output that you can connect it without stretching or bending the cable. You'll also need to have a power outlet nearby. A modem generally requires a coaxial cable to connect to the cable output, as well as a power cable to connect to an electrical outlet. Both of these cables should come with your modem, but if you bought it used, you may need to find replacement cables.  If you plan on attaching the modem to a router, you will also need an Ethernet cable. Consider buying a longer coaxial cable if the one that you have is too short to allow you to mount properly your modem. Each modem is unique, and yours may require additional setup outside of this article's capacity. Reading your modem's manual will help make you aware of any additional steps that you have to take to install the modem.

Summary:
Make sure that your modem will work with your Internet subscription. Find your room's cable output. Decide on a place to mount the modem. Make sure that you have all of the required cables. Read your modem's instructions.