Mission 01: Learn mission basics
Learn mission basics.
Team Up with Axel, search the underground passage in Twilight Town for the treasure chest, and collect its contents.
The easiest mission you can possibly accomplish, the game pretty much guides you through this one. Follow the tutorial instructions for jumping and camera movement. Leave the room through the door in front of you and head north. Take the first right into the room next door and leave through the opening on the opposite wall. Head north through the new hall; you know you are headed the right way as Axel will offer the tutorial on barricades. Follow the hallway left at the corner, and right at the next corner; you should see the chest at the top of the stairs. Head there to trigger the chest opening tutorial, as well as the backpack tutorial. Open the chest and claim your Potion to complete the mission.
Axel will then tell you about the Return To the Castle (RTC), opening the RTC tutorial. Head back the way you came. If you so desire, you can open the gate in the northern room on the way back, making a little shortcut back to the dark portal. Choose to return to the castle, and you are done... you didn't even have to defeat a Heartless!