Slope intercept form is y=mx+b, where m is the slope and b is the y-intercept. To turn x+2y=-4 into the form you are asking for, you have to isolate y. The first step to accomplishing that is to subtract x from both sides.
2y=-x-4
Next, you divide both sides by 2 and you'll have slope-intercept form!!!
y=-1/2x-2
The slope is -1/2 (remember, rise/run) and the line intersects the y-axis at point (0,-2).