Congrats on the new rig.
The OS should be on the SSD, if not, they royally screwed up. If it was a Dell I'd be worried, some are okay/good some are horrendously bad, but not so much with Ibuypower, it should be setup right.
Regarding the drives though, there are three ways to easily manage two drives like this....You can do it however you want but my advice is pick ONE of these and stick to it, otherwise your data will end up scattered all over.
The first is just use it to store your big things like movies, music, photos, this is simple and easy to manage.
The second is move your entire profile there, this is a bit more hassle however if you ever need to reload the OS, all your stuff is still safe on the second drive. The downside though, again, this is a bit of a hassle to setup.
The last way, and how I would recommend doing it is using it for games installs (not game save data)
On the HDD create a "games" folder then after you install your game launchers (steam, etc) and before installing any games configure them to use the HDD/games folder as the default install location. Why is this better? Your photos and movies rarely change, so it doesn't put wear on the SSD. Games on the other hand get massive updates quite often, you change them out etc. Another reason for this method is HDDs fail FAR more often than SSDs, your game installs are easy to replace if you lose the drive, your personal info is not.