Think of any number, say 1.
Substitute 1 for x in

                2x+y=6 
              2(1)+y=6
                 2+y=6
                   y=4

So one point is (x,y) = (1,4)  <-- that's one solution.



Think of any other number, say 4.
Substitute 4 for x in

                2x+y=6 
              2(4)+y=6
                 8+y=6
                   y=-2

So one point is (x,y) = (4,-2)   <-- that's another solution.


Think of any other number, say 0.
Substitute 0 for x in

                2x+y=6 
              2(0)+y=6
                 0+y=6
                   y=6

So one point is (x,y) = (0,6)    <-- that's still another solution.

Think of any other number, say -1.
Substitute -1 for x in

                2x+y=6 
             2(-1)+y=6
                -2+y=6
                   y=8

So a fourth point is (x,y) = (-1,8)   <-- that's a fourth solution.

Plot the solutions as points:



Now get a ruler and draw a line through them:



That's the graph.

Edwin