The intercepts of any equation are where the line crosses that axis. For an x-intercept the coordinate point would look something like (x,0), for any value of x. The y value would have to be zero to intercept the x-axis. The same for the y-intercept, it would look like (0,y) because the x value would have to equal zero.
So to solve your problem substitute zero in for the x value first and solve for y. That would give you:
1/2(0) - 2y = 4
0 - 2y = 4
-2y = 4
y=-2
So y equals -2 when x equals 0. Your coordinate would be (0,-2), that's your y-intercept.
Same thing for the x-intercept, we can find that value by substituting 0 for y:
1/2x - 2(0) = 4
1/2x - 0 = 4
1/2x = 4
x=8
So x equals 8 when y equals 0. Your coordinate would be (8,0), that's your x-intercept.