Playing a single file

Go to your drive and long press on a media file to access file options. Tap "Play" to play a file.

Playing all files in a folder

Step 1: Tap the three dotted line at the top right corner of the bar.

Step 2: Tap "Play All"

Playing Multiple files at once

Step 1: Tap the three dotted line and choose "select" 

Step 2:  Select the files you want to play. You can also select multiple files. Tap "Play" to play files from your drive.