Fallowing :
If I am going to use both an SSD and a hard drive in my computer, would I need to buy windows for both the SSD and the hard drive? If not then how does windows get on both drives?
No.
You do not need or want the OS on both drives.
The second one, the HDD, is just there as space to be used. It does NOT need an OS on it.
Multiple drives are very, very common and recommended. My main system has 5 drives. My HTPC has 2.