Read your textbook please.. it should have quite a good explanation there.
In short, you should say that it enables us to efficiently & economically produce ammonia, then you should say why? For example, it adopts a temperature which is a compromise between high equilibrium yield and high reaction rate (you can't have both in the ammonium production reaction) and provides a method of re-using the unreacted reactants (remember, since it's a compromise, a significant amount of the reactants that go out of the reacting chamber has not all reacted to form the intended product). I think the choice of the catalyst is part of the Haber process as well, but I'm not sure.
Then you might want to explain why the Haber process has enabled large-scale production of ammonia, which in turn is used for fertilisers, bombs, etc. Before, they used other substance for fertilisers and bombs and that substance started to run out as it was used extensively... I can't remember what that is, although it's in my Conquering Chemistry textbook and it has chosen itself to go to a hiding place tonight (well I left it at school).