If you don't or can't have a WiFi network in your house or office, you can send data between computers or other devices and a modem connected to the internet, using the ordinary mains wires in your home.
These homeplugs plug into ordinary wall sockets but have an ethernet socket to connect to your computer.
This bundle includes two homeplugs + the bridge to connect your router to them. Some short ethernet cables and instructions.
See https://www.solwise.co.uk/solution-homeplug.htm for more on this technology and manufacturer, though these are probably not the most up to date models.
Solwise Homeplug Local Area Network / Ethernet Bridge (Hamsey Green CR6)
This offer has been gifted to someone and is no longer available.