No Kloofnek, there is ONE hard disc (!TB), split into 3 partitions. There is no point in backing up the data on your C drive to either the D or E drive, because it is one single piece of hardware. If you have a disc failure you will lose all three discs.
Depending on the model of your laptop you may, or may not, have room inside for another hard drive (you will need to buy a caddy to put it in, if you have). Your best option is to buy an external hard drive and backup to that. They are not expensive and just plug into one of your USB sockets - you only need to plug it in when you want to backup and there is argument for leaving it unplugged at all other times as some malware seems to be able to get at all drives on your computer. You can buy a 1TB external drive for less than £50 - since your C drive is only 906GB that will clearly be large enough.