VSEPR is used to determine the 3D structure of a molecule by considering the structure around a given atom. This is accomplished by minimizing repulsions between electrons groups located about the atom. It must be kept in mind that not all molecules are simply one atom surrounded by a few others. Several individual applications of VSEPR are often to be considered before the structure of a molecule can be determined. Utilizing VSEPR requires four steps;
1) drawing a Lewis structure for the molecule in question,
2) counting the electron groupings about each atom and minimizing the repulsions between them,
3) determining the positions of atoms and lone pair electrons in the molecules and
4) naming of the molecular structure as a result of the positioning of the atoms (note the more complex a molecule the less likely that the whole molecules structure can be named but merely the geometry around the central atoms).
Though you are already expected to know something about Lewis Structures this tutorial should give you a complete stepwise example of how to approach questions dealing with VSEPR. A simple case will be followed by a much more complex one.