To find the y-intercept, set x = 0 and determine the value of y. It's 4. We could be more formal and write the y-intercept as (0,4).
To find the x-intercept, set y = 0 and determine the value of x:
0 = -(1/2)x + 4, or (1/2)x = 4, or x = 8. Formally, (8,0) is the x-intercept.