Cut a 2 x 3 for the rear leg. Make the piece slightly longer than the desired height of the easel.
Cut the two front legs out of the 2 x 3s slightly longer than the rear leg. Angle the end cut to 15 degrees so that the front legs will form an inverted "V." Cut a larger degree angle for a bigger span between the front legs.
Put all three legs together, with the rear leg in the center. Drill a hole the same size as the bolt through all of the legs a few inches from the top on the widest size of the lumber.
Place the bolt through the holes, then cap with a washer and nut. Determine the angle of the easel by moving the rear leg back and inclining the front legs before tightening the nut.
Use the 2 x 4 for the tray that will hold the canvas on the easel. Cut to any length suitable, but a standard size such as 24 inches to 48 inches will suffice.
Use wood screws to attach to the 2 x 4 a little less than halfway from the top of the easel. Again, this can be placed anywhere desirable.
With the easel standing and at a good angle, use rope and screws to attach the rear leg to the 2 x 4 canvas tray. This makes the easel more stable.
Sand all edges.