What is the app Time machine for or what does it do?

Tomba10 wrote:

What does the app on my MacBook Air desktop called Time Machine do and what's it for please?

Time Machine is an app that provides the ability to back up your data.

Back up your Mac with Time Machine - Apple Support

I would add that you are apparently not currently backing up and you need to. Eventually something happens and drives will fail. Unless you have a backup in place, everything will be lost. Time Machine does backups very well and backups should be stored on an external disk which is used exclusively for that purpose. When you set it up, carefully read and follow its instructions.