Each branch is the equivalent 10 knots and each half branch is 5 knots. As regards direction, think of the feathers as those on an arrow.
From page 38 of the SD Manual:
SkyDemon includes wind aloft forecast data which is automatically downloaded for the area of your route, and this extends to 25,000 feet and 24 hours ahead. As you plotted a route you may have noticed coloured wind feathers appearing on the main map at regular intervals and tailwind/headwind indicators in the background of the virtual radar window. If you don't see these, ensure that the Wind button on the weather toolbar is ticked, or for tablet/smartphone users tap the Weather menu and toggle ‘Show Forecast Wind Aloft’ on.
The date and time and the level represented by the wind feathers defaults to the date, time and level of your flight, as set in Flight Details.
Nexus 7 (2013) – Android 6.0.1 & SD 184.108.40.206984
Huawei P30 – Android 9.1.0 & SD 220.127.116.11984
PC – Windows 10 (Home Ed) Version 1909, Build 18363.657 & SD 18.104.22.168