Question

operating a toothed section jack stand
raising
the cup of a toothed section jack stand can be raised freely. letting go of the cup will cause it to drop and stop at the next loc
locking
this type of axle stand is locked when the cam in the top of the jack stand slides into the toothed section, preventing the cupped section from dropping further. if the cup is at the correct height, the steel pin is inserted as an extra lock.
lowering
check that the vehicle weigh is not sitting on the jack stand, before lowering the cup. if the cup needs to be lowered, the steel pin needs to be removed from the jack stand. then hold the cup with one hand and move the steel handle upwards using your other hand. the cup can now be eased down.
what causes the jack stand to lock, if the cup moves down?
as a result of the lowering, the steel pin moves between the toothed section and the jack stand, effectively locking the section.
the cam causes friction between the toothed section and the jack stand, so the cup does not move down any further.
the cam slides into the toothed section, locking the cup.

Explanation:

The text states that this type of axle stand is locked when the cam in the top of the jack stand slides into the toothed section, preventing the cupped section from dropping further.

Answer:

The cam slides into the toothed section, locking the cup.