Humans have 46 chromosomes altogether.
Autosomes - 22 pairs (homologous) chromosomes which play no part in sex determination. The last pair 23rd, are the sex chromosomes and these determine the sex of the individual.
Girls have two X chromosomes (XX)
Boys will have an X and a Y (XY).
Difference between autosome and sex chromosome
Autosomes are the somatic chromosomes which control the body characters or somatic characters, Whereas Sex chromosomes are the allosomes which determine sex of an individual.
For instance, in man there are 46 chromosomes in which 44 chromosomes are the autosomes and 2 chromosomes are the allosomes,
Male ------ 44 A + XY
Female --- 44 A + XX