Back Up

Sorry but I can not find any threads that solve my problem! New to the Apple wonderful world, but sometimes confusing.
How do I back up selected files each time I have used a specific software?
If I use the iCloud the whole iMac is backed up?

Best regards from a summer warm Sweden and, tomorrow we will have abt 30 C, lovely temperature.

If you are have set up and are using Time Machine, then everything that has changed is automatically backed up every hour.

Here are instructions on how to set up Time Machine:

How to set up Time Machine in Mountain Lion | Macworld

The iCloud service does not back up your iMac, just certain settings and things like iTunes Store or Mac App Store purchases. It can also be used to sync settings and important info (like calendar and contact settings, that sort of thing) between Macs and iOS devices like iPhones and iPads.

Greetings to Sweden from Western Canada, where we are having a mild but mostly sunny summer!

Happy I am.
Thank you chas_m for your link. Didn´t know about the Time Machine.
I´ll try it tonight during a good and cold Carlsberg Black Gold, not only crack opened, the sixth it is.
Thank you and have an nice week end.