On Wind Rose, the blue triangle with an A is Apparent Wind Angle (AWA); the green triangle with a T is the True Wind Angle (TWA) and the smaller black triangle with a line is the indication of Course Over Ground (COG).
When your boat speed drops below 0.3 m/s, the COG triangle will disappear. When the boat speed is detected to be over 0.3 m/s, the COG triangle will appear.
There's another blue triangle with a number inside which is the water current vector indicator:
The arrow shows the direction of the water current relative to the boat.
The number is the water current speed in knots.
The current vector is calculated from your boat’s motion through the water compared with its motion over ground from GPS. The system also estimates and corrects for leeway (sideways slip due to wind) based on heel angle, so the result is intended to show water current rather than leeway, though a small influence may still remain.
Then, the red and green lines on the wind rose are laylines. They show you the two optimal courses you can sail to make progress upwind. Because a sailboat can’t sail straight into the wind, you have to zig-zag (tack) back and forth.
The green line marks the best course on port tack.
The red line marks the best course on starboard tack.
When on a route, the lines appear like this:
The black aim line matches the usual aim line chart colour. Refer to this article for more information.
Together, these lines form the “corridor” you need to stay within to eventually reach a destination that lies upwind. They save you from guessing when to tack and help you steer more efficiently toward your goal.