libwacom is a library to identify graphics tablets and their model-specific features. It provides easy access to information such as "is this a built-in on-screen tablet", "what is the size of this model", etc.
The name libwacom is historical - it was originally developed for Wacom devices only but now supports any graphics tablet from any vendor.
libwacom does not make a tablet work. libwacom is merely a database with a C library wrapper for information about a tablet. It has no effect on whether that tablet works.
libwacom is currently used by GUI toolkits (GNOME, KDE, others?) to map built-in tablets to the correct screen and by libinput to determine configuration options such as the left-handed settings. SVG layout files are used to describe tablet visually.
A common indicator that a device is not supported by libwacom is that it works normally in a GNOME session, but the device is not correctly mapped to the screen.
Use the libwacom-list-local-devices tool to list all local devices recognized
by libwacom. If your device is not listed, but it is available as an event
device in the kernel (see /proc/bus/input/devices) and in the X session (see
xinput list), the device is missing from libwacom's database.
Use the libwacom-list-devices tool to list all known devices and verify
the tablet is not in that list.
See this wiki page on adding a new device and how to test it.
The API documentation is available at https://linuxwacom.github.io/libwacom/