For building something like a big building or a parking garage, there is a need for a large flat surface of concrete. Wondering how they make the dirt and the concrete flat. It's hard to make a tiny flat surface at the beach in sand let along thousands of square feet. Wondering what sorts of machines tools or techniques are used at a high level.
For big constructions, there is a survey plan and a few bench marks marked and cemented by the surveyor. Then at the time of excavation there are auto rotating laser levels that cast a level moving beam which is easy to see and follow. there are reflecting mirrors and elevation readers.
Excavation is done in stages, from rough to fine contours using different heavy machinery depending on the type and configuration of the site. Many jobs call for presence of soils engineer at intervals to test the soils and determine their properties and if they match the project's soils report.
Concrete slabs can be leveled with vibrating, moving, or, rotating screeds or operator driven motorized finishers or manually. There are plastic stakes that mark the finish level and the have fittings for long aluminum levels.
Structural drawings usually call for 1/8" to 1/16" tolerance in slabs level.
Regarding Kamran's citation of laser leveling, note that this technique is also used to produce rice fields covering tens to hundreds of acres with very precise drainage slopes. In this case, the earth moving machine receives the light flashes from the rotating laser mirror and lifts or lowers the grading blade in response. The machine operator then simply drags the grader blade back and forth across the field to be leveled and as long as the laser can be seen by the grader, the required slope is produced.
Easier done than thought.
"Grading" and "levelling" are carried out in stages of approximation.
A grading machine or a common dozer can work up an even surface (horizontal or uniform gradient).
As for the good question, "It's hard to make a tiny flat surface at the beach in sand let alone thousands of square feet. Wondering what sorts of machines tools or techniques are used at a high level.": Remember that the surface of a liquid is always horizontal. A layer of concrete usually evens out the minor variations (bumps and pits), giving you a horizontal "flat" surface.