Beating the game is easy, just follow the simple missions, later you get to create your very own american chopper bike, it's not fun but atleast you get to drive it, and no you don't unlock anything that lets you build a bunch of custom bikes.

To do a great burnout, come to a complete stop... The press the front brake acceleration button, and steer the bike in any direction you want.

You can't make custom bikes for fun, You can only make custom bikes in career mode.