Hello, I'm new to Houdini and it looks like I need help now. I've searched everything that I could get free but didn't find anything related. Do you guys know, how to move vellum objects, like the hand in attached video? Thank you in advance.

you can use soft pin constraints with Match Animation toggled and painted stiffness to control parts of your vellum object with animated geo with varying strength
or you can also use forces, all depends on your exact needs
and for stuff like in the video you may want to use Tetrahedral Softbodies, those have also another advantage, that you can pin deeper internal points and the higher hurface points will freely jiggle
you can also combine it with shrinking restlength for hand pinned inside of the mouth that will pull in other parts of the hand

tamte
you can use soft pin constraints with Match Animation toggled and painted stiffness to control parts of your vellum object with animated geo with varying strength
or you can also use forces, all depends on your exact needs
and for stuff like in the video you may want to use Tetrahedral Softbodies, those have also another advantage, that you can pin deeper internal points and the higher hurface points will freely jiggle
you can also combine it with shrinking restlength for hand pinned inside of the mouth that will pull in other parts of the hand

Soft pin is Soft Body (SBD) Pin Constraint or Vellum Constraint Pin to Target? If it is SBD Pin then how to use it?

Vellum Constraint Pin set to Soft

tamte
Vellum Constraint Pin set to Soft

It works!!! You're really cool!!!