Papyrose101
De Kween of De Ugandan knuckles
The 1 in pink is me...Ugh so cute! >u< I can give you some tips, if you want!
When I was starting out with anatomy I used this tutorial! It's not super detailed but it's helpful!
The thing is, characters that are liked Sans, Papyrus, Undyne, and Toriel (and almost all the UT characters) are supposed to be anthropomorphic so they have more-or-less human bodies. You can legit just use human anatomy and edit it to be a little more goat (for Tori), skeleton (Sans/Pap), fishy (Undyne), etc.