Near where I live there is a large road and intersection construction project in progress. The intersection of Cole Road and Lake Hazel Road is being redone, and Lake Hazel Road will be extended eastward, and cross over the ~45 foot wide, century old, New York Canal via a bridge (which has not been built yet). The New York Canal takes Boise Project water from the Boise River to Lake Lowell in Nampa. It runs for ~40 miles. A few days ago a crew from the Concrete Placing Co. was also finishing lining the canal walls upstream and beneath the bridge. Lining the canal is less than 10% of the road project.
Lining the flat canal bottom is like a bigger version of putting in a sidewalk, driveway, or patio. You likely are familiar with that. The area is dug out, and the edges of the patio are walled with forms to contain the concrete. Then concrete is brought to the site by a mixer transport truck, and delivered via an attached chute (or with wheelbarrows). As is shown above, two guys use a 2x4 board as a screed to strike off the top of the concrete level with the tops of the forms. Then the top can be finished further with a float and edger.
If you wanted to demonstrate ‘striking off’ to a small audience you might use a 9” square cake pan as the form, a 12” long ruler as the screed, and a granular solid like kitty litter to represent concrete. Pictures or videos work better for a larger audience.
What about the sides of the canal? As shown above (viewed from one bank looking southeast) the sides were divided into panels ~12 feet wide. Half of them were poured using forms, and then the other half were filled in. You can see the welded steel wire reinforcement mesh laid where the new concrete will be placed. A chute from the concrete truck delivers a very stiff mix. Then a Deere tracked excavator uses a pair of ropes to pull a metal screed rod up the wall starting from the canal bottom. That rod is guided by two men using the panels already on both sides to support the ends. You also can see a concrete abutment for the new bridge at the very right.
The image of screeding came from Wikimedia Commons.