Every website will have it's own SSH login details which you can find on the websites dashboard. This will let you log in via SSH to the specific site with an SSH username and password.
In addition to user/password authentication for SSH, you can now connect using SSH keys.
Before you follow the steps in this guide you will need to generate yourself an SSH key. If you are unsure on how to do this please see some of the below links for reference:
Installing your SSH key onto your account
Once you have generated your key on your local computer you will need to install it in your profile.
First click on your profile and then select SSH Keys
Then click on Add Key and then paste your SSH key into the key details box and then click Add Key
Your SSH key should now show up in your profile as below:
Enabling access via SSH keys to your websites
Now that your SSH key has been installed into your profile you will need to add it to the sites you would like to connect to using it.
Navigate to your websites dashboard and click on the SSH option in the left hand pane:
On the SSH page find the Manage SSH keys panel and click the Add Key button
Find your SSH key from the dropdown list:
And finally click the install key button
You will now be able to connect via SSH to the server using the servers hostname, the websites username and your SSH key