I just got this mod called creature mounts. I can't figure out how
to mount them. I tried dropping it on my character and dropping
it on the ground. Can someone please help me?

Um. Don't know that one, could you post a link please?

That mod looks iffy. Have you tried abot's Guar mod? Creature Mounts doesn't even come with a sitting mesh, so my guess is that it may just remove your lower half or glitch you into the creatures. But I didn't check it out in game.

I'm not sure how to get it to work, the readme didn't say much...

The only mod I've seen called Creature Mounts is a mod that adds a merchant outside Seyda Neen selling stuffed animal mounts for house decoration, not mounts in the rideable sense of the word.