Fold tab Z over 90 degrees, so you can stand the tank upright. These parts represent spherical tanks which hold propellant. Repeat with the remaining tanks. The markings in the part's center, by the way, represent the mechanism which reeled out three restraining tapes to deploy the booms, which spring out, uncoiling, from their canisters. Find a letter printed on each protruding rectangle.
Tanks face up.
Secure with glue where each rectangle protrudes from a hole. Add a little more glue inside where the parts touch. Wait for the glue to dry. They should be centered within the six ports on the spacecraft bus piece. Fold the small tab Z up, away toward the printed side, about 80 degrees, on each of the two arms.