a versatile command-line tool that lets you communicate with a device. - Home

• Enable Developer options - find build number - tap the build number 7 times untils you see the message you are now a developer!
• Enable USB debugging on your device - Settings > System > Advanced > Developer Options > USB debugging
  • ADB Android Device Unauthorized

• How to list all the files in android phone by using adb shell?

• How to extract default ringtones from Android device? - adb pull /system/media/audio/
  • How To Transfer Ringtones From Android to Android

Debug server

$ adb kill-server
$ adb start-server

Applications

• How do I kill all active tasks/apps using ADB? - adb shell am force-stop <PACKAGE>

How do I get an apk file from an Android device?

see also

• Top 5 Ways to Extract APK File of Any App on Your Android Phone
  • Extracting APK directly from Google play]
  • from old device you can share link to application by email

# for system apps use -f -s to list path
$ adb shell pm list packages             # list
$ adb shell pm path com.example.someapp  # get path
# get it
$ adb pull /data/app/com.example.someapp-2.apk path/to/desired/destination

see also

• Android remote