You can use the standard SSH access protocol to open a terminal session on your Accelerator. Use your server's IP address or valid host name (domain name), and provide a valid username and password (see Account Logins and Important URLs). By default, you will login with admin@YOURPUBLICIP. The port 22 is default for SSH and does not usually need to be specified. When you login over SSH, you should be put in your home directory automatically, unless you override it in your SSH client configuration.
UNIX and Linux based systems (including Mac OS X) come with a built-in command line ssh client. For Microsoft Windows systems, there is always Putty, a good SSH client to download for free.
admin should have a BASH shell on your Accelerator. For security reasons, you cannot login to your Accelerator as directly root. Instead you can change to root, once login:
sudo su -
It is advisable to restrict the number of users who have full BASH shell access. You can create users with access to SFTP/SCPonly shell, if you only want to allow them to upload their files to the server (rather than making configuration changes).