When I try to add a layer mask either by clicking the icon in layers panel or going layer>add mask I am not getting a usable mask. The layer mask icon in the layers panel is added to the image, but it is still the rectangle with a white circle in it, not an icon with an all white or all black background.
Sounds like you have "No Thumbnails" set in Layer panel options, which displays mask icons as you describe. Right-click a layer icon (not a mask icon) and pick "Small", "Medium" or "Large" to see thumbnails.
Clicking on this icon does not produce a mask to paint, whether white or black. Can anyone help me understand why I am not getting the typical pixel layer mask that can be used to paint and reveal the image beneath? I must be missing something obvious but I can't figure out what I am doing wrong. Any help would be appreciated.
Clicking on a mask thumbnail/icon should target the mask (you'll see a white border at the corners of the current target's thumbnail/icon) to receive paint, adjustments, etc, but not display it as a grayscale image on the canvas. To see the mask in grayscale as well as target it, Opt/Alt-click its thumbnail/icon. Use Backslash key to toggle rubylith overlay of mask.