Classifiers
Handshapes that stand in for whole categories of things and show how they move.
Focus
A hand becomes a thing
A '3' handshape can become a vehicle; a flat 'B' a flat surface or a car's path; a bent 'V' a seated person. Classifiers show location, movement, and manner in a way no fixed vocabulary can.
Why this comes late
Classifiers are consistently among the hardest receptive skills for learners (they can't be looked up in a dictionary). They reward everything you built in Levels 1-3: handshape precision and spatial setup.
This is a grammar lesson — its skill lives in movement and space, not a fixed vocabulary list. Work through the focus points above, then bring them to the receptive drill, the tutor, and — above all — to real signing by Deaf creators, where these skills are actually learned.