Log-in via their web portal first using username (firstname.lastname@example.org) and password, and from there to gain access to the cPanel, you will need to go into “My Accounts” and then click on the red button that is marked “Go to cPanel”.
If you require to visit their knowledge base, you will need to head into the “Support” tab, from there use the search bar.
If you need to log a ticket, you will be able to do so from here. However, if you activate their chat [below], their support will log this for you. On the right of the screen, you will be able to track these open (& closed) via “View My Tickets”.
In a new tab, open the Siteground Website, (cannot be done in the same tab and cannot be simply from “New Tab-ing” a link) from here you will be able to access their chat support in the top right hand corner. Once there you will need to have the username (email@example.com) and the password ready.