In order to transfer files from your computer, you need to connect your Android phone as media device (MTP). To do that follow these steps:
1. On your Android device open Settings and go to Storage.
2. Tap the more icon in the top right corner and choose USB computer connection.
3. From the list of options select Media device (MTP).
4. Connect your Android device to your computer, and it should be recognized.
In certain cases, you might have to connect your Android phone to your computer, and switch between different connection options a few times before your computer recognizes your Android device as media device.