How do I do this please?

Sorry if I've posted in the wrong place, I did look around here first. I have the paid versions of both True Image 2013 and Acronis True Image Home 11 and I want to clone an external portable hard drive to another external portable hard drive. About 950GB in total and it needs to do it automatically without me doing anything more. If anything goes wrong on the original drive, then if I put in the backup drive, it should work straight away within a few seconds. Can anyone please let me know, in laymans language how exactly do I do that please?

Any help much appreciated.

Chris