You can't.
At one day old before all their organs fully tuck away after hatching you can use a magnifying glass and a bright light to try to spot the difference in their vent, but after the first day you can't sex them this way any longer. Any attempts to try could hurt the chick.
The only way to tell is to wait for comb development, behavioral changes, hackle feathers, sickle tail feathers, crowing, etc. Some chickens can be sexed by color but this is not one of those.