Find some graphing paper and graph away..
i.e. Sub in x = 0 and find what y = ?
y = 1/2(0) + 3
y = 3
So we know the coordinate (0,3)
When x = 4 , y = ?
y = 1/2(4) + 3
y = 4/2 + 3
y = 2 + 3
y = 5
So we know another coordinate (4, 5)
When x = -4, y = ?
y = 1/2(-4) + 3
y = -4/2 + 3
y = -2 + 3
y = 1
So we know another coordinate (-4, 1)
Putting it all together, the coordinates: (-4, 1) , (0, 3) and (4, 5) should be plenty sufficient to graph and then draw a line of best fit connecting them.