In the most basic applications, the 2x4 is set on edge and pulled backward (toward you) in order to generally smooth down the lumpy concrete. It helps to have two workers, one on each side. Aluminum screeds are often used, as they provide a straighter edge.
For more professional screeding, a motorized screed may be used that has a long handle to eliminate laborious bending and tugging.
Screeding is not the final finish. For that, you need a bull float.

