5th dnd – Does the fall count as a movement?

I am new to D & D. I have read some answers to similar questions to mine, but I wish further clarification.

Can I, as Winged Tiefling, fall on an opponent as part of an attack? And more precisely, is the distance to which I fall deducted from the count of my distance (speed)?

Example

I have a distance of 30 feet and I have 15 feet more than an opponent. I want to fall on him using my weight as a weapon. I then want to move 15 feet and cast an action spell, then move 15 feet (or 30 feet) as a bonus action and throw a Cantrip.
Would the 15-foot drop, because of its involuntary movement, cost me dearly, thus removing the second part of my movement phase?