how do I delete a folder or album in Photos?

If you Control (right) - click on an album and select Delete Album you will delete the album but not the photos in the album.

If you Control (right) - click on an folder continuing albums you will delete the folder and all album inside that folder but not the photos.

Hello spikejj,

We see that you're wishing to delete folders in your Photos app. We're happy to offer some assistance.

Our article Create albums in Photos on Mac includes instructions for deleting albums that you've created. For other issues you may encounter, the Photos User Guide is a great place to find those answers as well.

We hope this helps!

No, the sidebar is available at all times if desired. Go to the View menu and select Show Sidebar.

I have it enabled so the screenshot shows Hide Sidebar.