Drive a stake into the ground where you want the center of the gazebo. Tie the end of a ball of string onto the stake. Stretch the string out 60 inches, as indicated on a tape measure. Walk around in a circle to determine the perimeter of the gazebo. Make four marks on the ground, evenly spaced around the perimeter of the circle.
Dig four holes, each 18 inches deep, using a post hole digger. Pull up the stake in the center, and dig one 18-inch hole there. Place one 110-inch pressure-treated beam vertically into each hole around the perimeter. Place the 144-inch beam into the hole in the center.
Fill the holes with dirt around the beams, with a shovel. Use a level to ensure that the poles are straight vertically. Tap the dirt down firmly around the beams, with the end of a shovel.
Toss one canvas tarp over the top of the poles. Throw the other tarp perpendicular over the first tarp. The sides will hang down. Create a curtain effect by rolling them up and securing them with twine just below the tops of the posts.