If you didn’t add an animation and code in the animation when it walks, that is the problem, though if you did add an animation, try making your own, using other animations made by other players do not work.
I think the problem is not the animation, because the animation is playing correctly, but this humanoid is walking like walking on ice, or something like this, do you know why? Some solutions here in devforum say the problem is in the humanoid.HipHeight, but I changed and did not work for me.