To transfer any file, you just have to install the app on your computer and connect the Android device using a USB cable, selecting the MTP option.
From the window you can drag and drop files in a very simple manner. Once the transfer is finished, you just have to securely disconnect the USB cable to enjoy your files on your phone or computer.
Now, thanks to Android File Transfer, you can have a backup of the photos or music on your Android phone, or transfer any file to it from your computer.
If you want to upload music from your computer to your collection on Google Play, you should do so with the Music Manager application.