plz explain me primitive and centerd unit cell in detail...

Unit cell is the smallest portion of a crystal lattice which,when repeated in different directions generates the entire lattice.Unit cells are classified into two types-
1.Primitive unit cell – When constituent particles are present only on the corner positions of a unit cell,it is called as primitive unit cell.
2.Centerd unit cell – When a unit cell contains one or more constituent particles present at the positions other than corners in addition to those at corners,it is called centered unit cell.These centered unit cells are of three types-
1.Body-centered unit cells – Such unit cell contains one constituent particle at its body-centre besides the ones present at its corners.
2.Face-centered unit cell –This unit cell consist of one constituent particle present at the centre of each face,in addition to those present at corners.
3.End-centered unit cell – In this unit cell,one constituent particle is present at the cente of any two opposite faces besides those present at the corners.