I want to mirror my c drive to new drive in windows 7

i have 2 sshd set up as raid,o, c drive.in addition i have 4 hd,s set up as raid 5,or drive d,.i believe the purpose of the raid configuration was to back up data,from c ,which does all the work.i was looking threw my d drive and noticed only a few items that i choose to back up buy selection were on the drive no files or programs from c drive,so should there be a constant back up of c,going at all times,if,please help.but looking threw my disk manager if i right click drive d it shows option to make into mirror,i need to unallocated space on drive to create mirror.before i start formatting any hard drives could someone with some experience in this please assist, thank you new to raid and dont want   to caue any harm till clear understanding