Chicks can be vent sexed, wing sexed or sexlinked. Each of which not many average folks can do with success.
Vent sexing is just what hatcheries do..typically by highly trained people who know what to look for. Inexperienced hands can cause damage to the chick and are usually inaccurate in their guesses of what they see upon examination.
Wing sexing must be bred for. Breed a fast feathering roo to slow feathering hens and the resulting offspring are the opposite. The problem with this is most folks don't know if their birds are fast or slow feathering and then to match them up for wing sexing is not always possible.
Sexlinking works for various crossings to produce differing colors. The most common are barred rock, red sexlink and black sexlink. Unless you're breeding the right birds for sex linking, you will not succeed with this method either.
Sex linking is probably the easiest to attempt of the three. Most backyard chicken people just wait the 5-6 weeks to identify the gender of their chicks. Sex characteristics become more evident at that time.
Jody