a = 2 	in binary 0000 0010
b = 3   in binary 0000 0011

while loop (b is not 0):
data = a&b (& means AND. Keep the bits that exits in BOTH a and b). Data = 0000 0010
a = a^b (^ means XOR. Copies the bits if it is set in one or the other but not in both) a = 0000 0001
b = data << 1 (<< 1 means shift the bits left 1 place). b = 0000 0100

b is not 0 so do the while loop one more time:
data = a&b. Data is now 0000 0000
a = a^b. a is now 0000 0101
b = data << 1. b is now 0000 0000

b is zero so stop the loop.

Return a which is 0000 0101 = 5.  (Hence 2+3 = 5)!