Dig two holes, about 3 feet deep, as far apart as you would like the upright bamboo poles to be.
Cut two bamboo poles to the height you wish the entrance way to be, plus 3 feet. These will become your vertical supports.
Cut two more bamboo poles to the width you want your entrance way to be, plus 2 feet. These will become the horizontal supports of your entrance way.
Lay your two vertical poles on the ground, parallel to each other, with one end of each placed at the edge of the hole you dug in Step 1.
Lay your two bamboo poles from Step 3 across the vertical poles, with 1 foot overhanging on either side of the vertical poles. The two poles you have just laid down should be parallel to each other, 1 foot apart, at the opposite end of the vertical poles from the holes you dug in Step 1.
Lash the horizontal poles to the vertical poles by tightly tying some twine around them. Tie a knot around one pole, then wrap the twine around the two overlapping poles forming an X shape where they overlap. Wrap your twine tightly around the joint many times to give strength, do this for all four intersections of the bamboo poles.
Mount a rectangular sign (plywood) measuring 1 foot by the width between the vertical poles if you like, by nailing it directly into the horizontal bamboo poles.
Lift the entrance way upright and place the ends of the vertical bamboo supports into the holes you dug in Step1, then backfill the holes to secure the entrance way sign into place.