Gallery moderation is a great way to review guest uploads before they're visible to other guests in a gallery. To moderate guest uploads, you first have to turn the feature on.
Open the gallery you'd like to turn on moderation for
Click "Menu" at the top right
Click "Settings" on the menu list
Click the drop menu at the top left of the new window, and select "Guest Permission".
Find and toggle on "Enable Content Moderation"
Save changes
Once content moderation is turned on, new guest uploads will not immediately show in the gallery.
To review guest uploads, select "Pending review" in the gallery drop menu, to see a list of all uploads that need to be reviewed.
Select the ones you want to approve, and click "Approve". To select multiple files, first click the highlighted button shown in the image below, then click on each file you want to select.
You can also approve uploads when you're in the gallery file viewer. While viewing an upload, there'll be a 2-checkmark button if it needs to be reviewed. Clicking that will approve the upload.