This command controls moving your character upward. When flying or hovering, enabling moving up will cause your character to gain altitude. When not flying or hovering, your character jumps up.
The up command is optionally followed by an enable flag. up 1 enables moving up, up 0 disables. Once enabled, your character continues to move up until disabled, either continuing to gain altitude if flying, or endlessly jumping if not. If the enable flag is left off, the current state of the flag is displayed.