A formulation is a mixture that has been designed as a useful product. Unlike a mixture made by chance, every chemical in a formulation is there for a particular purpose. Formulations are made by mixing the components in carefully measured quantities, so that the product has exactly the properties it needs.
Many everyday products are formulations. They include fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods. In a paint, for example, the pigment gives the colour, a solvent keeps the paint runny enough to spread, and a binder holds the pigment to the surface once it dries. Brass is an alloy of copper and zinc. It is a formulation because the two metals are mixed in set amounts to give a metal with useful properties.
You may be asked to identify a formulation from information given. Clues are a list of ingredients, amounts or percentages of each, and a stated purpose. A pure substance has just one component, so it is not a formulation. You do not need to know the names of the components in particular branded products.