Its as simple as running
from a prompt. Followed by the password for shell access to your box.
If you have setup ssh correctly and have trouble connecting from outside your network, you are most likely behind a router which has a built in firewall, you probably want to port forward the settings so you can connect from outside.
Although its good practice to change the default port of 22 for ssh to avoid scanners from finding you, use a typically uncommon port.