Labelling drives as "C" or "D" is just a windows convention. Not used on Unix/Linux systems. Linux will list the primary drive as sda, the second as sdb, the third as sdc so if you are familiar with the English alphabet, you shouldn't have any problems. Partitions are numbered. sda1 would be the first drive, first partition, sda2 would be the first drive second partition. The windows method is a leftover from the early days of computing when the A and D drives were floppies so the first hard drive would be C.
If you don't know which drive is first in boot priority and the drives are the same size and you have the same number of partitions and size of partitions, you could have some problems.