"What is the difference between WCA and drift angle?"
Wind correction angle is basically the angle you need to compensate for in order to keep your desired track. If there's no wind your heading of 360 will probably be your track as well. If you have a wind from let's say 300 you might need to keep a heading of 350 in order to keep your 360 track. 350 is 10 degress less than your desired track, hence a WCA of -10 (steering 10 degrees to the left).
Drift angle is the actual influence of the wind on your aircraft's heading, measuring the difference between heading and track. If your heading is 350 and your track is 360 the wind is blowing you 10 degrees to the right, hence a 10 degree right drift. If your track is 002 degrees instead, the drift angle is 12 degrees right(+).
In an ideal world, WCA and drift angle is the same but with a different prefix, e.g. + or -.