as an adult you'll probably find it easy. Basic principles of physics are what make a bike stand upright once its moving... all in the same way as the spinning of a top.

Just sit on one on a gentle hill and let it start rolling (make damn sure your feet can drag to help stabilize yourself at first!). Then just steer. Then do the same thing on a flat road while peddling. Once forward momentum is established you're set.

Kids struggle to learn because, well, they're kids.