Determining a Kitten's Sex
Visual cues will help you determine if a kitten is male or female. While this distinction may be difficult to tell with newborns, it'll become easier the older they get. Knowing the sex doesn't make any difference in how you raise them, and only determines whether the kitten will eventually need to be spayed or to be neutered.
A male kitten's genitals will look circular in shape. Between the anus and the genitals, there will be excess fur and tissue where the testicles will form.
A female kitten's genitals will be closer to the anus and will look like a straight line or a teardrop. There will be less excess fur and skin between the genitals and the anus.
If you're new to kittens, you can simplify this by remembering male = circle, female = line.