How do I end the game?

How do you make it so when the player completes your game, the game ends?

The best way to do this is with a plotscript. You will probably want a plotscript anyway for making the ending sequence. To end the game, just use the plotscripting command game over.

plotscript, end the game, begin   
  game over
end

For more info on plotscripting, see the Plotscripting page.

While you're making an end of game script, you may want to add some extra effects, like playing music and/or showing a back drop or textbox.

Note that if you attach a backdrop to a textbox and wait for the textbox, just before the player returns to the title screen the player will see the hero on the map for an instant. So you might want to use the showbackdrop command instead.

plotscript, end the game, begin 
  play song (song:game over)
  show backdrop (2)
  show text box (45)
  wait for text box
  game over
end

Without using plotscripting

If you don't want to use plotscripting, another simpler way is to make a text box that says "Game Over" and link it to itself (using the Next box: property in the text box editor). This method does not automatically return the player to the title screen, they still have to pick "Quit" from the menu manually, but it is nice and simple, and makes it abundantly clear to the player that they have won the game.