Didn't pay enough attention earlier, so I'd like to point out exactly what's going on here.
Rights to Intellectual Property
I do hereby declare and agree to trade my rights of intellectual property Name(model name) _________________
to Pantera Entertainment in exchange for my name as contributing artist to be listed in the official Theme Park Studio game credits. I am aware that no other considerations or cash offer for these rights shall be considered. Pantera Entertainment shall keep these rights indefinitely and use them as they see fit.
I'd advise all artists to seriously consider the terms carefully before signing that form. Effectively, you are saying that you cannot use your work in other projects, such as whatever NoLimits or RCT park/track/custom scenery you may have. The alternative I recommend is releasing your under some CC/GPL license that enables commercial use, but I don't think Pantera picks up on those.
That said, many users are still struggling to get started. I'd recommend hitting a search engine, Youtube, and/or to go look for books that introduce the subject.