Jump Jets / Zoom - details and controls
The top left button on the Secondary Screen is the Jump Jet control or Zoom if your 'Mech is not equipped with Jump Jets. (see BattleMech Specifications to see which 'Mechs have Jump Jets)
Jump Jets are simple to operate:
Push button.
'Mech goes up.
Release button
'Mech comes down
Functionally, all the Jump Jets do is lift the Mech up. So, if you hit the Jump Jets while standing still, all you'll do is fly up and down in place. To "fly" over or on top of something, you'd have to be in motion before you hit the jump jets. So, move in a direction, then press and hold the "Jump Jet" button (Secondary Screen, top left button). The button fires the jump jets as long as you hold the button. If something impedes your horizontal motion (i.e., you hit a building or another mech), you will only "fly" up and down until you get to the ground and move horizontally again. Then you can re-fire your jump jets.
There is a limited amount of jump jet fuel at any time. As you "fly", you will see the level of that fuel indicated in the green bar to the right of the Auxiliary Display in the bottom of the Secondary Screen. When this indicator gets to the bottom, the jets will stop and the 'Mech will fall to the ground. (Don't worry, usually it will land on it's feet.)
The jet fuel is NOT limited in it's supply. It will regenerate and refill the tanks when not in use. You will be able to use the jets whenever there is fuel in the tanks.
The difficult part is learning how to master Jump Jet use. You have limited control of the "flight" in Basic Pilot Mode, but you have more control in Mid or Advanced Pilot Modes.
Read additional training notes from "Q" regarding the Use of Jump Jets
Zoom
Zoom is in place of "Jump Jet" when the 'Mech does not have Jump Jets. However, Zoom is only available in Mid and Advanced Pilot Modes.
Pushing the Zoom button toggles the Zoom window that will show in the HUD in the Main Viewscreen. It will show a magnified view so that you can more precicely aim your crosshairs on your target.
Downsides: It's harder to run and aim with the zoom. You can't use Zoom and Light Amplification at the same time.
See also Armor MFD and Joystick for details on trigger assignment of Jump Jets and Zoom.