I bought a Wacom Intuos CTL-4100 tablet. It connects via USB with my laptop. When I connected, it somehow worked, but a bit erratically. Also, GNOME Settings (Wacom Tables) could not find it (neither the table nor the stylus).
Fortunately, I found exactly the problem I had, when I noticed the LED on the table was dim, instead of bright. It seems the tablet was in "Android mode", whcih sends different commands. To change it back to "desktop mode", I only had to press the leftmost and rightmost buttons in the table for about 3 seconds. I noticed the light changed to bright, and now GNOME Settings perfectly found it, and it was no longer erratic.
There is a detailed description of the problem in "Issue: My Wacom Intuos (CTL-4100 or CTL-6100) has a dim status LED and behaves erratically".
Once GNOME Settings can find the tablet and the stylus, it is a matter of configuring them. For that, you can follow instructions in Wacom Graphics Tablet in GNOME Help.