You will need to configure port forwarding, and will need access to the Administration Panel on the router.
Log in as the Administrative user on your router, Usually by typing either:
http://192.168.1.255 considering what you have listed as your local ip-address.
Look through your settings and try to find Port Forwarding. This is where you can specify to permit access to unique machines within your LAN.
Here is a screen shot of my tab with one of my ssh settings:
There is a really good website (at least it's one I've liked using in the past) that has screen shots and other helpful info located here. If you'd like more specific help leave some comments and I will try and help further. You might be able to find your specific router in their list.
Once you find that, you just add the internal address that you want to permit access to, and specify the ports want them forwarding to (or range of ports).
So like in your example, where you already have identified your external address... after setting up the portforwarding for SSH with port 22 (which I wouldn't recommend). You would then be able to access your machine by ssh by typing:
If you decided to permit port 22 / or
ssh <username>@<the_address_you_viewed_on_whatismyip> -p <non-standard port#>
If you chose to use a non-standard one.