<1> you want to copy your source files for backup
A--> press the given comination of keys [Alt] + [F] + [A]
[Alt] for Alter, [F] for File & [A] for Save as
and then give a new name for file.
======= OR========
<2> you want to save a backup file with the help of operating systems
[you did'nt mention the operating system, please mention it.]