I am registering a game on a site so that I can sell it, and it needs me to put in my game studio. I work on my games in c++ and I dont't have a team, or a company. Can I throw out a name and be done with it? or do I need to have a registered company?
The simple answer is yes, unless the terms of service specify differently, you can just use any name you decide or simply use your own name.
However, if your games ever turn enough of a profit that it can no longer be considered a "hobby" then you must register as a business.
I have done such agreements in the past. Depending on where you live, an assumed title or company name may not be legally allowed. For all such agreements, I would put "independent" in that field.
However it's really best to consult with a lawyer who knows about the various laws surrounding this.