You can only pick your bus up at Port authority in Manhattan. 42nd Street and 8th Avenue.
Livingston Street greyhound bus station. Its behind Macy's. It takes you to Penn station where you have to transfer. Bus leaves Livingston street at 9am & 1pm for Penn station.
Their stop in Brooklyn is in Liverpool. you can google it ro get the full address. I think the bus picks you up from there and take you to Penns station in NY where you might have to transfer depending on where you are going.
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