Hi, so you are a bit confused. I get why.
Look on the bottom of your logitech keyboard.
See if you find this orange logo.
[image|1324972]
If you do find this orange logo, that means it supports what Logitech calls "Unifying Technology" where it easily pairs to the pictured receiver.
You can purchase one from here:
https://www.ebay.com/itm/Logitech-Unifying-USB-Receiver-PN-993-000439-Ships-from-USA/182316780766?epid=935416905&hash=item2a72ed4cde:g:CI0AAOSwYIxYBCA6
Once you purchase this USB receiver, you also need to download the pairing software.
http://support.logitech.com/en_us/software/unifying
Install the software, then plug in the USB receiver.
Run the software and follow the instructions.
It will tell you to add a device, and set the receiver into pairing mode.
To pair, simply switch off and on the keyboard.
Now if you don't have a power switch on the keyboard, you already know that this is not a supported keyboard. List the model number of your keyboard, not the name of it if these instructions don't work.