Do you see an Ethernet port on your computer? Connect one end of an Ethernet cable to the Ethernet port, like this:
Connect the other end of the Ethernet cable to your router. Now you have a wired connection (aka an Ethernet connection) to your network.
If you were thinking more of a wireless connection (aka a WiFi connection) to your network: Today, most motherboards already have a wireless network adapter built into the motherboard. You can check your motherboard's documentation to see if this is the case for you. Note: In order to use the built-in wireless adapter, you need to enable it in the UEFI (which was formerly known as the BIOS.)