Question 82964
y=3x
or 
y=3x+0
Compared to the equation of a line formula:
y=mx+b
y=any y value
m=the slope of the line
x=any corresponding x-value
b=the point where the line intersects the y-axis
For y=3x+0,
the line will cross or intersect the y=axis at (0, 0), starting from that point, use the slope of 3 or 3/1.  That is, from (0, 0,) go up +3 and over +1 and plot that point (1,3)
From (1, 3) go up +3 and over +1 and plot that point (2, 6).  
.
Now for the bottom of the graph, start again at (0, 0), and using the slope
-3/-1 (same as +3), go down -3 and to the left (-1); plot this point (-1, -3).
Repeat this pattern by going down -3 and over to the left -1; plot this point (-2, -6).  
.
Connect the lines.
.

y=x+3
or y=1x+3
The slope = 1 or 1/1
The line crosses or intersects the y-axis at (0, 3)
So, repeat the instructions from above, only start at point (0, 3) and go up 1 and over 1, etc. 
Graphing:
{{{ graph( 300, 200, -6, 5, -10, 10, 3x, x+3) }}}