A character model sheet is used to record the look and scale of your character. They aim to set a consistent look and act as a reference for all animators on the show. Model sheets will contain scaling guides and multiple angles of the character. Some model sheets also have specific hands and facial gestures.
Most model sheets have a side view, front view, and a 3/4 view to showcase the character. We use lines for establishing the proportions. Lines show consistent ratios.
I made a model sheet of one of my characters Slicker (I might improve it later):
Actual reference image of Slicker:
