I guess you are talking about the wind direction in Route planner ?
The so-called Wind barbs in More options window is the reference direction for the wind direction. The usual reference direction is the North direction, more precisely geographical North. Click North up to set this direction which means that North is shown toward the top of the map.
What does Bottom to top and Left to right mean ? These reference directions are used by pilots. You must imagine that you are flying from bottom to top or from left to right of your screen, even if on the map your flight has a another direction. Then these settings give the angle of the wind in relation to these directions