How to delete unwanted photos? Also, can you delete more than one at a time?

Sahidic, are you asking about Photos on a Mac or on your iPhone? I amassing, because the signature below your question is showing "iPhone 11, iOS 13", but your question is in the Photos for Mac forum.

Just in case you have been asking about deleting Photos from an iPhone - you can only delete photos taken with the camera or saved to camera roll, not photos that have been synced to the iPhone from a computer.

https://support.apple.com/guide/iphone/view-photos-and-videos-iph3d267610/ios

In Photos, tap a photo or video, then do either of the following:

• Delete: Tap  to delete a photo from your iPhone and other devices using the same iCloud Photos account; see Use iCloud Photos.
• Deleted photos and videos are kept in the Recently Deleted album for 30 days, where you can recover or permanently remove them from all devices.

To select several photos for deletion at once, select the first photo, then let your finger move across more photos. Or tap each photo in turn while you are selecting them.

To delete pictures from within Photos, go to the [All] Photos pane at the top of the left sidebar. Select the photo you want to delete and right-click it. At the bottom of the menu that then appears will be "Delete 1 Photo". Click that. The picture goes into the 'Recently Deleted' album from where it can be restored for 30 days (or a little longer sometimes).

You can apply the same process to several pictures at once. Select individual pictures by holding down the Cmd key while clicking on them. Select blocks of pictures by selecting the first one then holding the Shift key while selecting the last one.

If you try this process in an Album rather than the Photos pane, the drop-down menu shows 'Remove from Album' rather than 'Delete'.

There is more information in the Photos Help.

Stephen