Dig a hole the size of your basin. Place gravel at the bottom for drainage and to prevent erosion. Level and stabilize the basin.
Place the pump in the basin and stabilize it. Attach the threaded adapter to the top of the pump. Cut a four-inch length of copper tubing and insert it into the adapter. Attach the ball valve to the top of the tubing. Cut another piece of tubing long enough to reach the top of the birdbath and insert it into the ball valve. Tighten all the nuts with your crescent wrench.
Dig a trench one foot deep and six inches wide from the hole to the nearest electrical outlet. Feed the pump's power cord through the PVC conduit and set the conduit in the trench. The length of the conduit and trench depends on how far the fountain is from your power outlet.
Fill the basin with enough water to cover the pump. Cover the basin with wire mesh to prevent debris or trash from clogging the pump. Using pieces of wood or stone tiles, make a deck over the hole. The birdbath will sit on top of this, so be sure it's fairly sturdy. Leave space the beams of the deck so the pipe will fit.
Guide the largest terra cotta plant pot over the copper pipe. If the hole in the pot is not big enough, use a chisel or drill to enlarge it so the pipe will fit.
Continue stacking smaller pots onto the pipe until birdbath is desired height. Two or three work best for stability, but larger ones are possible.
Make a hole in the center of the plant pot tray if there isn't one and guide it over the copper pipe. Use a tray that's big enough to hang over the sides of the top pot.
Place rocks or a little gravel in the tray so the birds can get good footing.