"es" is a pronoun that usually substitutes a neuter noun.

Example:
Ist das Bett zu hart? - Nein, es ist nicht zu hart. (es = it  das Bett = the bed)

But:
Es gibt Pinguine.

The "es" in the above sentence has a different function. It isn't the replacement for a particular noun; instead it serves as the subject of the sentence without really meaning anything. This construction is frequently used in impersonal turns of phrase in which there is no other subject. It is comparable to "there is" or "there are".