Homework / test English Tech/Engineering Printing & Publishing laser engraving system

this question is for a paid translation test
(I am indicating it here as I don't see the specific field in
the proz interface)

This manual is describing, among other things, the loading of a plate

"Set the focus distance between the roller and the laser by adjusting the laser aperture position using the machine mounted dial gauge and the cross slide movement buttons.
Retract the indicator by pressing the focus button.
Then press the alt+L key to ***make the job live***. Close the guarding. Start the roller rotation using the roller button. Once the roller reaches the engraving speed, press the alt+R to run the job."

I don't understand this expression, could you please explain, if possible with an alternative wording?

thanks!
Elena