Help me omg wireless networks :(

Hello, i am sooo lost!!!!!!
my grandparents have a netgear wireless router and i have a pc up the stairs!
with no wireless facility so i have a belkin usb adapter... which i cant seem to find hardware for!! and when i do it doesnt bloody work!!!
so how do i sort this?
i am sooooo stupid when it comes to things like this and dont understand all the technical terms :(
please someone explain how it all works
thanks :)
sophs! xx