How to mark files in irfanview?

I need to sort photos. Right now I use Irfanview tool to look through images. I use Del key to move (delete) images into Recycle Bin. I use Del key on images I like, since there are many less than I actually took. I then restore them out of Recycle Bin into a separate folder. That folder is my selected images.

I hate using delete, both mentally (pressing delete on a good image eh...), and physically (what happens with bits on disk being moved into potentially volatile space).

Is there a way to press something else, not delete images, but mark them for ease for transfer to a separate folder?

Q: How can I tag a file during browsing?

A: See the Hotkeys help file page. Tag a file with X, untag with SHIFT+X, use SHIFT+Q to show all tagged files in Thumbnails window.

From the Official Irfanview FAQ