Tests, Allies, and Enemies

After the Hero has crossed the first threshold, the bulk of the story begins. Most of the story takes place in the stage Tests, Allies, and Enemies. During this stage, the Hero is tested in preparation for the Ordeal, makes allies who help him, and enemies who hinder him.
Tests: The series of trials the Hero goes through and overcomes help him prepare for the ultimate Ordeal. The Mentor may or may not be present at this stage. Tests include natural disasters/terrain that must be crossed, such as rivers, storms, mountains, etc. There can also be man-made obstacles, such as walls, tollbooths, checkpoints, etc. Also, with a Special World comes different atmosphere, rules, culture, and such, so the Hero must learn to live in the Special World as a trial. Every time the Hero passes the test, he knows a little bit more about dealing with the Shadow.
Allies: Along the way, the Hero makes friends. They may have a common goal, or just be along for the ride, or be special Allies called sidekicks. Either way, there is a sense of camaraderie and unity among the Hero and his allies. Sometimes there's a whole group of them, all working together to defeat the Shadow. (Think Fellowship of the Ring, etc.) The sidekick, or any Ally, can act as the reader by asking questions the reader would have, thus filling in important backstory or information crucial to the plot through dialogue.
Enemies: Of course, the Hero is also going to make enemies. They may be minions of the Shadow, or just characters with their own agenda. The goals of the Enemies clash or directly interfere with that of the Hero and his Allies, resulting in more trials. There is a special enemy called the Rival, who may have the same goal as the Hero, but is competing with him to achieve it first or better. The Rival may hinder the Hero's progress on the Journey, making him an enemy, but really he is out for the same reward.
The stage of Tests, Allies, and Enemies is arguably the most important of the Hero's Journey. In it he grows, learns, adapts, and prepares for the stages ahead.