Unfortunately, the best thing anyone can really say is learn the screen, because that's the only way to do it. As far as both ways go, they all will terminate at the gate to The Guy's Skull-shaped Fortress. However, to enter it once it is finished, you have to have beaten all 6 bosses. Three of them are accessible through the upper path. The lower path branches in to two and contain one boss each, and the SECRET PATH contains a boss.