SPECIAL KEY TOGGLES
To open the menu system, hit the "[" key. To exit the menu/cancel a selection, hit "[" again. To cycle through submenus[Characters, Items, System, etc], "Home" goes up, and "End" goes down. The "]" key will shift your current submenu one page. "Spacebar" will perform/select an action, such as choosing a character or item to use. The Up, Down, Left and Right arrows move your cursor around within the current menu[Left and Right have no use in the system submenu though].
In the characters menu, the glowing character represents the one currently in use, while you can move the cursor and press Spacebar to select the next person. When selecting an item, you will either get a second screen of characters[for one-character use items] or you'll hear a sound effect[for multi-character effect items].
Some characters [i.e. Nethra] have multiple forms they can take advantage of. When this holds true for a character, a yellow text message will appear below the menu indicating you can change their form, which is done with the "Look Left" and "Look Right" keys (Usually "Insert" and "Delete").
Note: Being in the menu will pause the player and the monsters' movement, and will also freeze up player/monster powerup timers. Additionally, both the player and monsters are impervious to damage when the menu is open.