When the tablet is recognised by the OS (you didn’t mention your distro nor LO version), i.e. when the driver is installed, by default, you tablet pen behaves as a mouse. Consequently, use the free hand tool ib Draw (looking like a pencil writing a curve) to draw anything you like.
To the best of my knowledge, there is no built-in tool in Writer to convert hand-written text to digital text. This may be the role of some interface software.
I am under Fedora and the needed packages for Wacom’s are kcm_wacomtablet, libwacom, xorg-x11-drv-wacom (I’m constrained to X11 because of my outdated graphics card).
It looks like package cellwriter can convert hand-writing to digital, acting like a keyboard. However, if you intend to enter math formulas, you’ll end up with an image, provided you do that in Draw. For other usages, perhaps CAD applications could help you (this would be an abuse, but perhaps worth a try). I use FreeCAD but I find my Wacom doesn’t bring much more then traditional mouse (considering my skill level in FreeCAD which is very basic).