You can transfer music onto Android devices using two of the native programs on your Windows 8.1 computer: Windows Media Player and File Explorer. If you're on a Mac, install the free Android File Transfer application to sync audio files onto your phone. There is also a free service called Google Play Music that lets you store music in the cloud so that you can listen to and download it on all of your Android 5.0 devices.
Transfer Music From a Windows Computer -- Windows Media Player
The native Windows Media Player app on your Windows computer is a handy tool for transferring music onto your Android phone. Connect the phone to your computer using the phone's USB cable. If necessary, swipe down from the top of your Android's screen and select "Media Device (MTP)" as your connection type. When you connect the phone to your computer, a popup dialog appears on your computer's screen prompting you to select which program you want to use to interface with the phone. Select "Windows Media Player," and then click the "Sync" tab on Windows Media Player. Drag and drop into the Sync window the music you want to transfer onto your phone, and then click "Start Sync."
Transfer Music From a Windows Computer -- Mass Storage Device
You can also have your Windows 8.1 computer treat your Android phone like a USB key or external hard drive, enabling you to drag and drop music files into any folder on the device you choose. Connect your phone to your computer using the phone's USB cable. Click "Open Device to View Files" on the popup dialog on your PC. If the popup dialog doesn't appear, press "Ctrl-E" to open the File Explorer program. Click your phone on the list of external mass storage devices, and then drag and drop the music files into the Music folder on your phone.
Transfer Music From a Mac
If your music is on a Mac, transfer it onto your Android phone using the free Android File Transfer application. Download and install Android File Transfer on your Mac, and then connect your phone to the computer using the phone's USB cable. If necessary, swipe down from the top of your Android's screen and select "Media Device (MTP)" as your connection type. Open Android File Transfer on your Mac, and then drag and drop your music files into your phone's Music folder.
Managing Music Using Google Play Music
The Google Play Music service lets you store your music files online so that you can access them from any compatible device with an Internet connection, including your Android phone. To use this free service, download and install on your PC the Google Play Music Manager application, available through the Google Play Music website. Log in using the Google account associated with your Android phone, click "Upload Music" or "Add Music," and then select "Download Music Manager." Once the program is installed, open it and click "Upload" to upload music to your Google Play account. Install the Google Play Music app on your phone. Songs you uploaded are located in the My Library section of the app. Touch the "Download" icon located next to the album or song you want to transfer onto your device. You can also use this app to download and purchase new music from the Google Play store.
Compatible File Types
Your Android phone only plays audio files saved in certain formats. Visit this page for a list of these file formats. The Google Play Music app is also only compatible with certain files types. In some cases, you can expand the file compatibility of your device by installing third-party music players.