ssh/scp on computer hooked up to router
I was wondering if anyone could give me some advice on ssh/scp stuff on a computer I have at home hooked up to a linksys router. For example when I'm home and I have my desktop hooked up to router through ethernet cable and my laptop running wireless I can transfer stuff easy through the routers ip of 192.blah blah blah. But when I'm away with my laptop I can't connect to desktop. I tried finding out ip of desktop by going to "whatismyip.com" and if gave me an ip address. Then I when I was away I tried using ssh.
first I started ssh on my desktop. /etc/init.d/sshd start
started it on my laptop when I was there
then I: ssh 242.192.132.13 -l bob
that isn't the exact ip but you get the point. And the cursor would just blink for a while and then no connect. So is my problem a wrong ip address or trying to run through router or maybe my commands are wrong its been a while since I used ssh. I have read the manual for ssh and scp and these have not helped so far and to be honest are quite dense I really just wanted to access my computer for an experiment for future uses.
Thanks for all your help.