The menu provides quick access to many of the interface windows in the game. You can access the Hero, Inventory, Inventory Bags, Skills, Quest Log, Map Travel, Map Area, Observe, Friends, Guild, Party, Score Chart, Help, Options, and Log Out window from this menu.
You can further customize your layout by dragging the icons found in the menu to anywhere on your screen to create a button for direct access to that window. This can be useful if you want to invoke a window using the mouse but without having to open the menu every time. If you decide to remove the button, just drag the button onto the menu button and it'll disappear. You can rearrange the location of the buttons at any time just by clicking and dragging them around.