If you haven't formatted your HDD and given it a drive letter, nothing can be stored there. By you or automated installers.
You also need to configure Steam if you want it to store games elsewhere, so for now you should assume the game is on your SSD.
You can set up a second library folder on Steam, and at instal time it lets you select which one to download/install to. It also lets you move games from one library to another, which is really convenient. You can keep games you're playing on the SSD and keep others aside until later in the HDD.