To use ssh on your server, you must have a plan with a calcul capacity, like the VPS plans, which allows providers to install an Operating System (Linux or Windows).

To ssh, you have to install Open Ssh Server in your server. The setup depends of the type of Linux distribution you have.
Then you open your Console (or Terminal) and enter this Linux command :
ssh the_vpsserver_username@the_address_ip_of_the_serve r -p the_port_number (by default, the port number is 22)

For exemple : ssh paul@ -p 7777
The server answers with giving you the RSA key fingerprint (the key fingerprint of your PC) and it asks you for the confirmation to continue the connexion. You seize "yes" then Enter.
The server asks you your user password. You enter it and ... it's done. You are now connected to your server via ssh.