ArcticNick

I have just got the trial version of Acronis True Image Home. I have looked through the user manual but I am unclear about something. Can you tell me please, if I want to take an image of my C/ drive onto a backup USB drive I have to let the software install a partition. -Will that process wipe out everything on the backup drive or will all my data remain in tact? Thanks in adavance, ArcticNick (from one Iceman to another!