In most chemical reactions the reactants combine to form one or more products and the reaction goes to completion. that means the reactants are all used up and you only have product(s).
However, in some chemical reactions, an equilibrium occurs where there are both reactants and products present. An example of this is the reaction of N2 + H2 to form NH3. This reaction takes place under high temperature and pressure and there is always a combination of all three substances present.
In an equilibrium reaction if there are more products present than reactants the reaction favors the products.
If there are more reactants than products then the reaction favors the reactants.