To get a complete shape of solid, its atoms, molecules or ions must be placed at some particular places or points. A crystal lattice basically tells us about the basic structure of those points. After the correct placement of atoms on those points the original crystal structure is obtained. Each single point in a crystal lattice is known as lattice site or lattice point.
Here is a basic formula for crystals. i.e.

Basis + Lattice will give you the complete crystal structure. Basis can be simply described as the combined molecule formed by the combination of atoms. A simple diagram of lattice is shown below. The colored locations are the atoms.