Sending files through router

I have got a broadband moden connected to a router, the router then connects to 2 different computers. It works fine as both computers have access to the internet now. But I dont know how to send files from one computer to the other through the router, if I even can do this...
Anyone know anything about this sort of thing?

read up on File and Print Sharing

I had a similar problem with four Dell computers and a Netgear wireless router. In my case these 4 computers were using that wireless router and I couldn't share any folders. All were using XP home. But the two that I wanted to share files on were right next to each other and also they were only about 5 feet from the router. What I did was disable the wireless cards in each and connect them with patch cords into the back of the router. Then I made the logons the same. For example I used logon "Fred" and password left blank. Then I shared a folder on each one of them and this ran me through some process and took about 4 minutes. After that I was able to move files through the router. However I did the same thing on one of the computers that wasn't connected with patch cord, just wireless, and that one I was never able to share files with even though it had the same logon and password as the others. Because of this I'm guessing that the firewall in the router was stopping it. Just a guess. All the the computers, wired and wireless, are able to get on the internet.