Accessing individual computer from outside (newbie)

I have a router assigned an ip address with 3 computers on my network at home. If I want to be able to accept ftp connections on 192.168.0.101 on my network how can I let my router know that I am trying to access that certain computer.

I have 3 computers and if I try to ftp the IP address of my router how does it know which computer I am tryin to connect to? If it doesnt then how can I access one of my computers that is behind a router? Thank You.

You can assign/forward different TCP ports to your machines. In your router you should have an option for NAT/Virtual Servers. You can designate internal ports to which incoming requests will map.

Suppose you have two machines 192.168.0.1 and 192.168.0.2. You can assign global/external port 21 to your 192.168.0.1's ftp (21) port. You can also assign say port 1000 to your 192.168.0.2's ftp port. FTP requests made to your Global (internet) IP address will be forwarded to 192.168.0.1. FTP request at port 1000 will be forwarded to your other machine.

Hope this helps