Please help me, I really do not know what is backup and what does it do?

I know only this, backup copy your Operating System, programs, files, videos etc. Whenever computer dies/ damage, unable to start then backup helps to restore your all current material.

I come to know about Windows backup, and its contains "System Image" & "Repair Disc", that I do not understood, therefore never use that and backup.

At the time of purchasing laptop, shopkeeper gave me 3 RECOVERIES CDs and suggest that they are EXTREMELY IMPORTANT and you should keep them in safe place and use whenever your laptop fail to work. It occur 2 times, unable to start, I inserted CD, but nothing happened, therefore I rushed to Service center and fixed that. But now in August my warranty going to be over, therefore next time they will charge.

Recently I purchased an external hard drive for backup and it contains its own backup software, I run that backup, but confused that it do not contains System Images or Repair Disc.

I am average user of computer and fresher in this techniques.

After reading above, I only wants to ask that what should I do? Which one should I choose, either Windows Backup or External Disk Backup?

And also what should I do if computer failed to start or stop working, what are home remedies to fix that with help of these Disks and Backup.

Thanks.

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