There is, there are, there was, there were: how?

[autumn zenith]

Devant la maison, il y a un jardin. (In front of the house, there’s a garden)
What does il y mean? Why exactly "il y" what il (he) is doing here?

[kindred iron]

The il is impersonal, so it doesn't refer to anything. It's the same as the impersonal "it" in English. Think of "it rains".