the OS came with that last system I bought already on the hard drive...am I going to need a disk to install or can I just do it from the hdd? also how do I then move it to the sdd? can I do that during the install?
In that case you will need to purchase a new copy of Windows, the product key that comes with the system will be OEM, only good to use on that motherboard.
An installation disc isnt entirely necessary, it is possible to install Windows off a USB drive or the like, but you wont be able to do it off the other HDD no.
When installing the OS, have all other HDD/SSD's disconnected, Windows has a bad habit of putting files on other drives during installation, and kicks up a fuss if they go missing.