After you've connect the phone to the computer, you'll likely have a notification on your phone. If you press that, you should be able to change the type of connection you have to the computer, one of which being "File explorer" or something similar.
After you've chosen that, you should be able to see the phone on the computer via the My Computer icon. Double-clicking that should show all the different folders on your phone, allowing you to drag and drop your music files (preferably to a folder named "Music" or similar).