>"Working the negative or positive" .... what does that mean ?
The "positive" part of a move is when you are working against gravity to lift the weight (ie: the 'curl' part of a biceps curl, or the "lift" part of a lat row, or the "lift' part of a lateral raise, or, if you are using machines: the 'push down' part of a triceps push-down, etc.). The "negative" part of a move is when you are working in the same direction as gravity, resisting the lowering (usually) of the weight (ie: the 'lowering' portion of a bicep curl or a lat row or a lateral raise, or on the machine, the 'release hands up' part of a triceps push-down).
In relation to the step-ups/leg-presses, the 'positive' would be when you are pushing up onto the step. The "negative' when you are lowering down from the step. With hover squats, the positive would be when you are standing up, and the negative when you are sitting down.