When editing content via the back-end administration area of Mura, or using the "Full Edit" feature from the front-end public-facing view of your site, the various fields that are available for content items are grouped together within tabs. You can think of the Edit Content screen as simply one, giant form, because that's essentially all it is.
If you see a down arrow on the far right of the listing of tabs, simply click the arrow to view the additional tabs. This occurs when the browser is too narrow to display them all within the browser's viewport.
Note: If you don't see one of the tabs specified in this section, the group(s) you belong to may not have been granted access to those tabs.
Your site may also include tabs not identified in this section of the site. If so, your instance of Mura CMS is most likely using a custom plugin used specifically to create custom tabs and fields unique to your organization's needs.