Learner's definition of ACTIVATE
to make (something) active or more active: such as
to cause (a device) to start working
Touch the screen to activate the system.
activate and then deactivate a mechanism
A loud alarm was activated [=set off] when he opened the door.
The camera is activated by pushing a button.
The bomb was activated by remote control.
to cause (a chemical reaction or natural process) to begin
to order (soldiers) to serve in a war