When you connect the Device, Android Studio shows a notification on the remote device (here Redmi 5A). If you select Allow Debugging From this computer: COMPUTER KEY
, Android Studio will show the device in the list. If not selected, you have to disable USB Debugging and start it again and this is the main problem here in your question (as said in the log)!
Also see that you use USB for transferring files!
Also if you have done this correctly, try staring the adb sever again. Open the terminal window by clicking Terminal on the bottom of Android Studio.
Then type:
adb kill-server
Then type:
adb start-server