The service details will vary depending on your specific location.
The Mediacom cable modem is just as fast as the Comcast DSL modem.
The cable modem can be faulty, check with you service provider
In order to activate your service the cable company must know the MAC address of the cable modem you have installed.
The cable modem that you got from your service provider is adequate. You might get a little faster service with another modem but it will probably not make much of a difference.
You would need a cable modem when you want to connect to a cable internet service.
The cable modem allows the cable provider to plug their service into the back of the modem(coaxial cable) versus the DSL modem allows the phone company to plug their service into the back of the modem(phone line). The DSL service typically requires you to have a separate phone number from your main land line.
Yes, you can own your own cable modem, but most television and internet providers allow you to use a cable modem for free if you sign up for their service.
You can buy the cable modem itself but you have to have a service provider for it.
No. A modem is used for dial up.
Call your cable modem service provider and have them run a series of tests on your line. If necessary, they will replace your modem, as well.
Your question presupposes that you have subscribed to cable internet service, and that the provider has run a cable to your home. It also presupposes that you have a cable modem. If these suppositions are correct, you just have to run coax between the cable jack on the wall and the cable modem. Then you need to connect the modem to your computer via USB, FireWire, or whatever interface your modem and computer have in common. FriPilot
Data Over Cable Service Interface Specification (DOCSIS)