Basically, the remote control must be coupled or paired with the aircraft. This connects the two and the drone can receive commands from the remote control. Depending on the drone and software, this can be done in different ways.
Mavic Pro and Mavic 2 Zoom / Pro
If you are using the DJI Go 4 app, you can normally perform the pairing there. However, it also works without the app and smartphone, the
You can find more information about the individual drones under the respective