Ethernet Port How To Use Router When Modem Only Has 1 Ethernet Port?

How to use router when modem only has 1 ethernet port? - ethernet port

I have my cell phone today on my laptop. The router I am left into the modem via an Ethernet cable. The problem is that my modem only has 1 Ethernet port, I have connected my desktop with him. The modem also has a USB port, so I can buy a USB Ethernet adapter and it works?