If there are any active projects on the server, they will be represented in the list under the "projects" headline. Every project has their own environments for managing content and users for editing it.
Below the project list are some basic server diagnostics to help you identify potential problems, or to determine whether the server might be overloaded from hosting too many projects. It will take a lot of projects for that to happen, so most people shouldn't worry about that.
For content authors
The only button relevant for you is the "CMS" button. So go ahead and click that to get started.
You can create new projects, environments and backups with the "+" buttons and modify them with the "..." dropdown menus.
To access the backups dialog, click the "..." dropdown menu in the top right of a project and click "backups". You can then upload, create, restore, download or delete backups. An important thing to keep in mind is that all content on all environments will be replaced when restoring a backup, so it's always a good idea to create a new backup first, in case the changes are drastic.
The backup only restores settings, content and schemas to the project, it doesn't publish anything. You can republish the content tree in the project CMS.