ADB
Android Debug Bridge — the command line tool connecting your computer to an Android device over USB or the network.
It has three parts: a client on the computer, a server that mediates, and a daemon on the device. With it you install apps without a store (adb install), read the system log (adb logcat), copy files and get a shell on the device.
Access requires USB debugging to be enabled in developer mode, which in turn is unlocked by tapping the build number seven times — one of Android's odder but more durable design decisions. Since Android 11 there is wireless debugging over wifi, which avoids the cable but requires pairing with a code.