External Drives come with software now to help people sync the data, (for the less techincal).
You could also just manually copy the data by clicking and dragging.
I'm kind of a command line junkie so I use robocopy in scripts.
If you want something simple that just copies / syncs the files. FreeFileSync is the best free one.
There are also Backvp2 and GoodSync with more features, but they are paid.