i tried making the HumanoidRootPart the cube, but nothing happens, please help!
I've seen a tutorial on this on youtube by GnomeCode. He shows how to make a custom player model, which I'm pretty sure is what you mean by " cube character ". A player model that is a cube.
How to create, rig and animate https://www.youtube.com/watch?v=x2MFFBvIF6Y
How to change character while in game https://www.youtube.com/watch?v=pVD-HBlfv4g