Cut two cedar or redwood tomato stakes to the height you want the trellis to be. Make the cuts on the flat end, not the pointed end. Remember that 12 inches will be underground.
Cut the lattice panel to the height of the tomato stakes, minus 12 inches. Cut the panel to the width you want the trellis to be.
Lay the lattice panel on top of the two tomato stakes so the top of the lattice is even with the top of the stakes. Use an electric drill to insert wood screws through the paneling and into the stakes. Place one screw every 10 to 12 inches.
Pick up the trellis and take it to the garden. Drive the pointy end of the tomato stakes into the soil at a depth of 12 inches.