When you click on those parameters in the editor there is a description at the bottom of the property bar that tells what it does. The speeds are in pixels/second and the accelerations are in pixels/second^2, and sustain is in milliseconds as I recall.
Anyway you'll have to look in the source to see exactly what it does. It also has some other things it handles such as being on a moving platform and such.
Roughly off the top of my head the motion is done like this. On top of that you'll need to detect collisions and resolve them someway.
not on ground
--- add gravity*dt to velocityY
global number upPressTime=0
on up pressed
--- set upPressTime to time
up is pressed
time < pressTime+sustain
--- set velocityY to -jumpStrength
left is down
--- subtract acceleration*dt from velocityX
left is not down
velocityX < 0
--- add deceleration*dt to velocityX
right is down
--- add acceleration*dt to velocityX
right is not down
velocityX > 0
--- subtract deceleration*dt from velocityX
every tick
--- set velocityY to min(velocityY, maxFallSpeed)
--- set velocityX to clamp(velocityX, -maxSpeed, maxSpeed)
--- set x to self.x+velocityX*dt
--- set y to self.y+velocityY*dt