  We present a study of the young population in the starburst galaxy NGC 253.
In particular, we focused our attention on searching young star groups,
obtaining their main properties and studying their hierarchical organization.
For this task, we used multiband images and their corresponding photometric
data obtained with the Advanced Camera for Surveys of the Hubble Space
Telescope (ACS/HST).
  We have first derived the absorption affecting the different regions of the
galaxy. Then, we applied an automatic and objective searching method over the
corrected data in order to detect young star groups. We complemented this
result with the construction of the stellar density map for the blue young
population. A statistical procedure to decontaminate the photometric diagrams
from field stars was applied over the detected groups and we estimated their
fundamental parameters.
  As a result, we built a catalog of 875 new identified young groups with their
main characteristics, including coordinates, sizes, estimated number of
members, stellar densities, luminosity function (LF) slopes and galactocentric
distances. We observed these groups delineate different structures of the
galaxy, and they are the last step in the hierarchical way in which the young
population is organized. From their size distribution, we found they have
typical radius of $\sim 40 - 50$ pc. These values are consistent with those
ones found in others nearby galaxies. We estimated a mean value of the LF slope
of 0.21 and an average density of 0.0006 stars/pc$^3$ for the identified young
groups taking into account stars earlier than B6.
