Question 101374
ok first solve for y
x + 2y = 8
2y = 8 - x
y = 8/2 - x/2
y = 4 - x/2
Ok now we have it solved for y  but we need to tweak it a little to get it into a proper slope intercept form which is:
y = mx + b   where m is the slope and b is y intercept
So first lets place the x term in front of the 4
y = -x/2 + 4
Ok next take a look at -x/2 and realize that -x/2 = {{{(-1/2)x}}}
make that change and now we have this:
{{{y=(-1/2)x+4}}}
Now we have it in proper slope intercept form and we can easily see that the slope is {{{-1/2}}} and the y intercept is 4. And we are now ready to graph the line.
Start with the y intercept which is 4. Locate this on your graph by starting at the origin (0,0) and going up 4. Make a dot on your graph at this point (0,4). ok next we will use the slope to find the next point on our line. 
The slopes are given as {{{rise/run}}}. Rise occurs on the y axis and run occurs on the x axis. The slope of our line is {{{-1/2}}} so from the point we just plotted on the graph (0,4) we are going to rise -1  and run 2 then make a dot on the graph at this point (2,3). Now just to be clear rise -1 means move down 1 on the y axis and run 2 means move over 2 places to the right on the x axis. The rise can go up or down the y axis depending on if the slope is positive or negative, but the run is always to the right.
Ok so now we have two points on our graph (0,4) and (2,3). Only thing left to do is take a straight edge line up the two points and draw the line.
Here is the graph.
{{{ graph( 300, 200, -7, 7, -2, 7, -(1/2)x+4) }}}