Rooting Samsung Galaxy sDuos s7562 I followed the steps mentioned in the link below:

http://www.androidrootguide.com/2014/01/root-samsung-galaxy-s-duos-s7562.html#comment-45216

I got an error on step 13, where we need to install SuperSU from recovery mode,

while installing the Update-SuperSU v1-1.80 (which i downloaded from http://download.chainfire.eu/370/SuperSU/) it gives the following error message:

— Install /sdcard– Finding update package… Opening update package… Verifying update package.. E: failed to verify whole-file signature E: signature verification failed Installation aborted.

android android-resources samsung-mobile
Sounds like you are using the Stock Recovery. In which you won't be able to flash the SuperSU that you downloaded because it will not pass the signature validation. 

You will need a custom recovery, or some other way to install SuperSU as a system app on the device.