as far as - do not understand

[panicmonger]

Push it right down, as far as it will go.

Could you please tell me the meaning of the sentence above, especially the last part?

What does it mean by "go"?

Thank you very much indeed, grateful to you & appreciate your help.

[Barb_D]

Push it until it will not go any further.

As far as = as much distance as
it will go = it is capable of moving