acronis true image home 2010

i found out about this software as bb stores, so i thought that it would be an excellent software to use to backup my laptop. I have had so many problems with this laptop in the past. i have downloaded the atih 2010 trial version onto my laptop to try to back it up to a wd external disk drive, however i only have usb 1.1 instead of 2.0, i started the backup left home for a while and then came back and my external wd harddrive was turned off. my laptop was still running. i have looked on the wd external drive e and i found the following file underneath my backups.
systembackup_11_12_20091, 876,544,000 bytes or about 876 mega bytes.
when i go to my computer for my c drive and click properties i see 12,555,223,340 bytes used space and 147.475.971.872 bytes free space. can someone help and explain what i have backed up here. it apears to me that there is only 876 mb out of 12,555 mb backed up on my usb drive. I would like to be able to restore my computer and desktop with all my programs back to its original state.