Question 930135
Choose an x value. 
Say {{{x=0}}}.
Calculate the y value.
{{{y=3(0)+3}}}
{{{y=3}}}
Plot the point (0,3).
Now the slope measures change in y divided by change in x.
In this case, for each 3 unit move in y, you move one unit in x.
So starting from (0,3).
(0,3)+(1,3)=(1,6)
Plot the point (1,6).
Draw the straight line connecting the two points.
You can also just keep picking x values and generating y values but for a line you really only need two points.
{{{drawing(300,300,-10,10,-10,10,grid(1),circle(0,3,0.3),circle(1,6,0.3),graph(300,300,-10,10,-10,10,3x+3))}}}
Done.