"To turn the key" means to start or initiate a process or action. It refers to using a key to unlock or activate something, often metaphorically representing the beginning of a new phase or the starting point of a task.
Sentences with «to turn the key»
I saw a video describing similar problem caused by starter relay, but in that video the engine, ABS and gas lights were turning on when turning the key, mine does NOT. (mechanics.stackexchange.com)
The only way to fix is to put the car in park and then turn the engine back on turning the key in the ignition. (mechanics.stackexchange.com)
They decided to go with a simple home button and physical page turn keys on the left and right hand side. (goodereader.com)