They work by creating tiny air bubbles in the wet mix. MicroAir is one brand. Very small quantities are used. In mixing concrete you try and get all the dry particles in the mix to be wetted. The aim is to use as little water as possible, because water not chemically combined stays in the dry mix and causes weakness.
Plasticizers help to wet the surfaces, enabling the mix to use less water.
One brand is Pozzolith. Tiny amounts are used. Latex additive is sometimes used in concrete, adding it to the water first. Pigments or dyes can be added to the mix, or applied to the surface of set concrete. Special dyes are made for this purpose as common pigments can be broken down by the alkalinity of the cement.