You've installed Windows on a PC but the ethernet controller (part of the network card) is not supported "out-of-the-box" by your Windows installer so you now need to use a 2nd PC to download the correct network driver and put it on a USB stick.
Here is how to do it:
Step 1) Right click on "My Computer" and select "Manage"
Step 2) Click on "Device Manager"
Step 3) Look in "Other Devices" for "Ethernet Controller" with a yellow question mark
Step 4) Right click on "Ethernet Controller" and choose "Properties"
Step 5) Click on the "Details" tab
Step 6) Look at the "Device Instance Id" String
It looks something like
The important parts are VEN and DEV (Vendor and Device)
Step 7) Go to and you can look up the vendor of the device and then go to their website to find the correct driver download.
For a lot of network cards VEN will be 8086 which is the code for Intel.
The website for their driver downloads is