A catalyst increases the rate of a reaction without being consumed in the reaction.  The use of a catalyst does not affect the position and composition of the equilibrium of a reaction, because both the forward and backward reactions are sped up by the same factor.
For example, consider the Haber process for the synthesis of ammonia (NH):
:N + 3 H ⇌ 2 NH
In the above reaction, iron (Fe) and molybdenum (Mo) will function as catalysts if present. They will accelerate any reactions, but they do not affect the state of the equilibrium.