Paint the shed with a muted green weatherproof paint.
Choose trellises to fit each of the three sides of the shed. Set them against the sides.
Dig post holes about 16 inches deep at the points where the trellis "legs" will be. Drive a wooden post into each hole. These posts will be used to support the trellises.
Drive nails through the legs of the wooden trellises and the posts.
Plant several climbing plants such as ivy or morning glory at the base of each trellis wall. Typically plants should be spaced 2 to 3 feet apart but you can plant them closer for more dense growth.
Train the plants up the trellis by weaving and securing the vine tendrils with twist ties. When securing the twists, be sure not to make them too tight. Leave room for the plants to grow.