By installing the official Android File Transfer app on your Mac, you can connect your Android device to your computer and transfer files to it. Once connected, you'll be able to browse through all the files on your Android device, just as you would folders on a Mac. You can also send music files from your iTunes library to your Android device.
Step
Part 1 of 3: Installing Android File Transfer Program

Step 1. Click the Safari button on the Mac computer

Step 2. Visit https://www.android.com/filetransfer/ via Safari
Type https://www.android.com/filetransfer/ into the address bar of your web browser and press Return.

Step 3. Click the “Download Now” button

Step 4. Click the “androidfiletransfer.dmg” file in the “Downloads” folder

Step 5. Drag the Android File Transfer icon to the “Applications” folder
Part 2 of 3: Moving Files

Step 1. Connect Android device to Mac computer via USB

Step 2. Open the Android device screen
You must keep your device open in order to access the saved files.

Step 3. Swipe down on the screen to open the notification panel of the Android device

Step 4. Touch the USB option on the notification panel

Step 5. Touch “File transfer” or “MTP”

Step 6. Click the “Go” menu and select “Applications“

Step 7. Double click “Android File Transfer”
The Android File Transfer program may run automatically when you connect your device to your computer.

Step 8. Click and drag the file to move it
When Android's storage space is displayed, you can browse and move as many files as you would any other folder on your computer. When moving files to or from an Android device, the file size is limited to 4 GB.
Part 3 of 3: Adding Music from iTunes to Android Device

Step 1. Click the iTunes button on the Mac computer
You can find this icon in the Dock.

Step 2. Right-click one of the songs you want to send
If you don't have a mouse with a right-click button, hold down the Ctrl key and click an entry.

Step 3. Select “Show in Finder”

Step 4. Mark all the music files you want to send
You can select individual files or entire folders.

Step 5. Drag the selected files to the Android File Transfer window

Step 6. Unmount the files in the " Music " folder

Step 7. Wait for the file to finish moving

Step 8. Disconnect the Android device from the computer

Step 9. Touch the Music app on the Android device
This application may differ depending on the Android device you are using.