Accessing the Internet
If you want your computer to be on the internet then you need a paid service from an internet provider.
The usual way for this to work is for a broadband connection via your telephone line. This shares the telephone line with your internet usage, and does not impact your use of the telephone.
Connecting your computer to the Internet
The usual way for this to work is for your computer to be connected by a cable to a device called a modem which is plugged into your telephone line. So one end of the cable is plugged into the modem, and the other end is connected to your computer.
a broadband connection via your telephone line. This shares the telephone line with your internet usage, and does not impact your use of the telephone.
A wireless connection to the Internet
The modem plugged into the telephone line can be replaced by a device a called a router. This allows one or more computers to be connected without cables to the internet.
Each computer needs a USB network adaptor which communicate with the router allowing multiple computers to use the inernet simulataneously.
It also allow people to move their computer to different places, perhaps the garden on a sunny day!