The standard is the vertical. Its cups set the lift heights. Order the length that reaches the working deck plus the required handrail, not the storey height of the building.
The ledger sets the bay length and ties the standards together. The transom supports the board or steel plank across the bay. Braces stop the frame from racking. Leave any one of those out and the assembly is a pile of tube, not a working platform.
Base jacks take the uneven ground. Boards or steel planks make the deck. If the first order names those members separately, the crew can erect the first bay without a second call to the yard. The 3D Cuplock viewer on this site is there to make that list visible before mobilisation.