The exploration of each of the Soul Arbiter's Maze levels rests on the same set of rules. Each time the portal takes you to a new area, you'll be forced into a battle with monsters tied specifically to it.
Upon arriving at a particular level, you'll need to decide whether you'd like to reach a room with a treasure, or go to the next level without delay. The former involves one substantial drawback - you'll have to fight more battles. Nevertheless, I recommend taking the effort to go to the treasure rooms, because even if you don't find anything valuable there, you'll at least gain the always profitable XP.
To explore a level, go through portals selected based on the information in the acquired Soul Arbiter's Scrolls, or in this game guide. Here's a short explanation on how to read the scrolls: N stands for going through the north portal, S stands for going through the south portal, E stands for going through the east portal, and W stands for going through the west portal.
For example, if the scroll (or the guide ;)) tells you to use the north portal, go to the one with the letter "N" above it (the above screen).
If instead of an arena you find yourself in front of a staircase, it means that you've reached the last area of the current level (the above screen). When you go down, you can use the portal on the floor to get to the next level automatically.
The game doesn't force you to complete the ten levels on your first go. If you wish to leave a particular level, feel free to use a special portal on the main arena or simply pause the game and select to end the play. In the latter case, though, make sure to get to the staircase mentioned earlier so as not to have to start that level all over again.
Once you return to the room with the mysterious tome, you can interact with it, select the level you want to go to (the above screen), press SPACE and stand by the central portal again.
[TIP: Leaving the maze is a good idea also if you're running out of potions. The game doesn't allow the use of the world map in the room with the tome, but you only have to move to the next one to unlock it. Unfortunately, when you go back to the Soul Arbiter's Maze, you'll have to go through the area with interactive handholds again.]
[TIP: On the subject of restocking supplies, keep in mind that bashing pots and crates as you go through the levels can get you some fresh Health and Wrath Potions.]