We all started out clueless

I'm assuming you are working on the products page here.

Go to the products page in the editor. You will see, to the right, the page and layer gallery. for the pop up layer you wish to edit press the "S" (for solo mode) just to the left of the padlock and eye icon.

You can now drag images from windows onto the current one to change it. Select "T" from the toolbar or press "T" on the keyboard to enter text edit mode.

Press "S" again to leave solo mode.