Transferring files from your Apple Mac to an external hard drive has two main benefits; it enables you to backup important data and it frees up space on your computer’s hard drive. The size of the file determines how long the transfer from Mac to hard drive will take. You can choose from two methods for transferring files from the Mac to an external hard drive; each has its advantages and the right approach depends on your file management preferences.
Plug in the external hard drive and switch it on if necessary. External hard drives typically switch on automatically once powered up.
Connect the external hard drive to the Mac. The connection method varies according to the make and model of the hard drive but you’ll typically use either a USB or Firewire cable. Check the hard drive spec sheet if you are unsure. When connected the hard drive appears as an icon on your Mac desktop. If the drive has a name, this appears under the icon.
Hover your cursor over the icon dock and move it to the far left, click the "Finder" icon to launch Finder. Alternatively, click "Command-F" to launch Finder.
Type the name of the file you wish to transfer into the Finder search box. If you don’t know the name, browse your Finder folders to locate the file. If necessary, click the yellow button towards the top of the Finder window to reduce the window size so you can see both the Finder and the hard drive icon.
Click the file icon and drag it across to the hard drive icon. A progress bar will appear if the transfer takes more than a couple of seconds. Depending on your Mac preferences, you may hear an alert to indicate that the file transfer has finished.
Using Time Machine
Connect the external hard drive.
Click the Time Machine icon in the top left of your main menu panel. This is the looped arrow with the central exclamation mark.
Select “Back Up Now.” This automatically backs up all the files created since you last backed up. It also backs up programs, settings and and preferences and acts as a system restore point should your Mac hard drive crash.
Click the icon again and select "Enter Time Machine." This enables you to navigate the hard drive as if it were a file directory on your actual machine. From here, you can view all backed up files.