Nah..you're fine. You are correct about the center line. The closer you are to the 'ding,' the closer your shot is supposed to be to where you aimed (given wind and a little randomness mixed in). The farther left you miss the 'ding,' the more your shot will miss left....and vice versa.
I can't tell you what the lines represent, technically. But, I can tell you that between the 2nd and 3rd lines will produce a wicked shot that kind of starts left and curves left.....or a 'draw.' Some players can use that shot with amazing accuracy. Not I.
Why do the lines squeeze together? Well, as in real golf, the more power you use to swing the club, supposedly the harder it is to hit the ball straight. So, the narrower channel sort of represents that part of a 'real' swing.
Another couple of terms that may help you along these lines: Precision and Forgiveness. When looking at new clubs, you will notice the dots measuring how well a particular club(s) perform(s). The 'precision' dots measure how close to deadly accurate your shot will be when you hit the 'ding.' The 'forgiveness' dots measure how close to 'decent' your shot will be when you miss the 'ding' by a good bit.
Happy swinging.