How do I share internet from a USB Modem using a Router?

I've done it before but then I had my desktop reformatted and I couldn't retrace the steps I took. I have a USB Modem and a Belkin N Router. Previously, I connected the USB Modem to my desktop and the desktop was connect via Ethernet to the Router's modem input. The router successfully transmitted the internet wirelessly to my other devices. I need help in recreating this. I don't mind keeping my desktop on the whole time I need the internet. Please help! I need my Wi-Fi back. Thank you!