How to attach a photo? I don't see them in finder.

Yes, that is normal.

It is not possible to browse photos in your photos library using finder. That is what the photos app is for.

You can of course use finder to browse individual image files not contained in a library. So for example, if you wanted to export files from the photos app to a folder, you could do that, and they would be visible in that folder using finder. You could also attach them to any app or website from that folder.

To export photos from the photos app, select them, and go to the file menu>export

It would help if you would be more specific. For example, what are you attempting to attach a photo to? Your second comment makes no sense. You say "cannot find photos in finder". What does that mean? What photos? If a photo is on your desktop, you can see it. Are you talking about the Photos app? If so, that app is located in your applications folder. If you wish to have finder access to the app, then drag its icon down to the Dock and that will place an alias of the app there.

Hi

If you are uploading to (for example) Facebook, you click the attach picture in Facebook, then in the resulting browser, you scroll down to the media section, and choose photos. Like this...