The initial point is (0,0). [There should be arrows above each of the vector names below.]
Plot the point (3,-1). a is the vector that begins at (0,0) and ends at (3,-1).
Plot the point (2,2). b is the vector that begins at (0,0) and ends at (2,2).
If you add these two vectors together: a + b = (3-1) + (2,2) = (5,1).
In either order: b + a = (2,2) + (3,-1) = (5,1).
You get the same terminal point either way.
The terminal point of a + b is (5,1).
If you draw the vector from (0,0) to (5,-1), you have draw the resultant vector.