Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
What version of Android are you running? With Android 6 and later, the default USB option was set to 'charge only', but your tablet will still show up under devices. When you plug in the tablet, pull down the notification bar and choose the USB notification. you should see an option to connect in MTP mode. Select that and your files should then be available to copy.
BTW, the next time you plug it in, it will revert back to 'charge only' so you'll have to do this each time.