Where your website lives
Everything the web serves comes from public_html inside your home directory. A file at public_html/index.php is served at the root of your domain.
You will also see logs and tmp beside it. Leave those alone — the panel and the server write to them.
In the browser
The Files tab browses your home directory. You can upload, create folders, rename, change permissions, compress a selection to a .zip, extract an archive, and delete several files at once.
Text files up to 2 MB open in the built-in editor. Ctrl/⌘+S saves. Larger files must be downloaded, edited locally and uploaded again.
Over SFTP
The container overview shows your host, port and username, and a ready-made command:
sftp -P <port> <username>@<host>In FileZilla, choose protocol SFTP, enter the host and port shown, logon type Normal, then your username and password.
The port is specific to your container — it is not 22.
If you have lost the password
Use Reset SFTP password on the container overview. The new password is shown once and cannot be retrieved afterwards, so copy it before leaving the page. The old password stops working immediately.
Permissions
Files should be 644 and folders 755. The panel sets this correctly for anything you upload through it. If you have uploaded files another way and the site returns a 403, check permissions first.