What is the most easy way to back up files?

With the development of society, most of people usually use the PC to work. Obviously, it exits many potential danger. For example, many important e-mails or information are lost incidentally.

We should back up our information in addition to happening misfortune things.

Some of my friends tell me one way. Download some data backup software to back up your files is a good choice.

But i also want to know there is other way to solve this problem.

If you know how to solve this problem, please reply to me.