Distillation is a process used to purify a liquid that is contaminated in some manner. In simple distillation, you are dealing with one volatile material tht you want to have by itself. Distillation involves heating the liquid to its boiling point, then condensing the vapors, and collecting the purified liquid.
For example, you may have some water that also contains salt or other substances but you want just pure water. By using the distillation process you can end up with pure water. You would put the salt water in a container, heat the container to boil the water, and then pass the steam through a condenser (a cooling coil) where the steam is converted back to liquid water. The cooled water is then recovered as a pure substance.
In fractional distillation you generally have a mixture of volatile substances with different boiling points. A good example is crude oil which contains a wide variety of different substances with a wide range of boiling points. The crude oil is introduced into the bottom of the fractionation tower and heated. As the various materials in the crude oil reach their respective boiling points they evaporate and rise up into the tower. As they rise, the substances with the highest boiling points cool back to liquids first, while those with the lowest boiling points rise the highest before condensing. By removing the various condensed liquids at different points along the height of the fractionation tower, the original crude oil can be fractionated into useable materials.
Depending on the purity of the materials required, a number of fractionations may be done to isolate the specific substances desired.