If you intended to latch your newborn, usually every 2-3hrs or when LO cry for milk/latch.
Additionally you can use hand to express or pump whichever you prefer(I only use hand express, never used a breast pump), when LO is sleeping exceeded the latching time or when you feel that your boobs is “full/filled” with breastmilk.
The more you latch, the more your bobs will produce breastmilk.