When you sign up for Cable TV you may be provided with up to three services and those services are delivered to you on a single coaxial cable. There's television channels, telephone service and a connection to the internet.
Conceptually, let's imagine that inside that coaxial cable there are three pipes and each pipe will deliver one of the services. The device that the cable company provides to separate out these services in your house is called a "modem". The coaxial cable from the cable company will connect to your (their) modem and there will be connections on the back for each service.
The first savings for you to be aware of is the cost of that cable company provided Modem. Yes, their installer comes into your house and plops this "modem" down and connects it up for you. Here's the surprise, they charge you a monthly FEE for providing that modem! My cable company charged me $12 per month!!
After I did a little digging, I found a list on their website, of modems that you could buy and eliminate that charge. They offered to sell me the one that they brought to my house originally for $165. Since I had already paid $12/month for years, that sounded like quite a bargain. Then I went on Ebay and found the exact same one, new in the box, for $35.