The flanking pieces will be driven into the ground just a bit more than 1/2" apart. As soon as they're secured, insert the central pipe between them and join the three together, using copper wire.
In lieu of copper wire, you could also use silicone sealing "tape" for this step. I put "tape" in quotes because it's not really sticky so much as it's stretchy (although it does adhere to itself). This product is also good to have on hand in case of leaks at the pipe joints (it's true purpose in life). When using silicone sealing tape, stretch it tightly as you apply it over the joint, and keep it taut as you unwind it. Wrap it several times over the joint, allowing each successive layer to adhere to the last.
I found another use for silicone sealing tape. Since the rubber hose from the pump can't be soldered to the elbow, the tape can be used to add some stability at this joint. But doing so isn't critical to the project's success, since the joint in question will be underwater, anyhow.
The last major step is to connect the pump's rubber hose to the plumbing pipe. Insert the hose into the elbow that you've soldered to the short "intake" pipe (at the bottom of the plumbing). Note that this connection is easier to make if the elbow you used at this joint has a bend wider than the typical 90-degree angle.
On Page 10 we'll look at a different version of the completed garden fountain from the one I showed you on Page 1....