Check out tutorials for modeling and animating in Blender, importing it into Unity. There’s several discrete steps. I have personally done all of them and it took about an hour or two to learn, but probably a lifetime to master.
Roughly,
You make the model geometry in Blender3D (or your favorite 3D authoring software)
You rig the model geometry by creating an Armature and fixing bone weights
you paint and/or texture your model (optional)
you make some animations (optional)
you import the blender file into Unity
This would be for Legacy, but if you meet all the criteria (enough bones) to do humanoid, you can do that.
With Legacy the anims drive the geometry armature directly.
With Humanoid the anims drive the Avatar, which then drives the armature. (this is Mecanim)
In all cases the SkinnedMeshRenderer will realize the animated geometry and render it.
Remember: nothing says you have to import animations (Step 4 above); you can make them straight inside of Unity, and in fact it’s not a bad place to do it. Plenty of tutorials too.