This tutorial shows how to make an A using object snaps.
When entering a point value is is possible to snap to parts of existing objects.
Start the line function, and enter the first point of the left leg of the A as -1,2,0 by typing or using the mouse. And to enter the upper point of the left leg, just pick it off the viewport using the mouse with no snap, at about 0.6,1.6,0.
Now, say much later
you want to start another line beginning at the end point of the second point of the
left leg. You don't care what the point is, all you care about is that
it be the same as the point end of that line. To do this, turn on the line end
point snap using
the endSnap function 
.
Make sure the grid snap is off,
as it will override any object snaps. Start another line to begin drawing the right
leg of the A. Move the cursor over the left leg line. If the line end snap is on and
the mouse is over a polygon, the cursor will jump to the closer of the lines end points.
Make sure the cross hair is yellow. If it is not, the object snap is not taking effect.
Pick the first point and now turn on the grid snap and pick the second.
To draw the center of the A,
turn on the line middle snap option using
the middleSnap function 
Move the mouse over each line, snapping to the middle of each.