Every file inside the Documents tab has a magnifying glass icon with a popup titled Preview. Clicking on it will open the file viewer. If you are the creator of the document, you will be able to rename the file or add a description or alt text for accessibility.
There are checkboxes next to each file name; you can click them to select multiple files.
Clicking Preview with more than one file selected will open them all in the file viewer.
Left and right arrows on each side of the document, as well as clickable thumbnails along the bottom of the viewer, will allow you to navigate through the files.
From within the file viewer, click Download in the top row to download the currently viewed file, or click Download All to download all files currently being previewed in the file viewer.
You can also download documents without previewing them. In the Documents tab, click the download icon next to any file to download it individually:
Alternatively, click the checkboxes as described above to select multiple files, then click the Download button in the top row to download all selected files.