I've seen people use assets from Sonic games, I think that you have to put Segas copyright information before the game starts if you want to use it. But I feel like I need a full tutorial on how to simply start. What is the best way to start making games?
You need explicit permission from Sega if you wish to use their assets, if you use them without permission you would be breaking the law. (Yes, people break the law and get away with it all the time, but that doesn't mean that you are guaranteed to get away with it)