you can start with something really easy like a bouncing ball
That's where I started ^u^ (not to say my 3D is all that good but thats where we started in 3D animation class)
I basically just move things around and then keyframe em XD
The task here if i recall properly was just to animate a ball with a tail jumping across something so that you could challenge yourself to animate the movement but I went ALL out XD
This was the final i think.. been like 7 or 8 years since i graduated lmao so dont quite remember, but ofc like always I went all out XD and it was super fun but most of it was just literally moving around spheres, cylinders, rhombus's
Here's some more 3D I did - but these are all rather simplistic, like maybe you can try just animating a few fingers or just the hand and get the hang of it most of the time i literally just moved the arms/legs/ slightly rotated the body and that was like half the movement https://youtu.be/E4xPMOioLfw?feature=shared
but good luck! 3D can be really fun! you can sculpt better than i can