To develop on an Android device, you first have to enable the developer mode on it.
I have a Nexus 5, but the process is the same for whichever device you have.
First, we will go into the Settings of the phone and select About phone.
In About phone, we will scroll all the way down and stop on Build number. We will then tap on Build number seven times to enable developer mode.
Once we are done, we will get a notification saying that our device is enabled as a developer device.
If we tap on it again, it will show a message saying No need, you are already a developer.
Now, if we go back to the settings page, ...