Evaporation is the process by which water (and other liquids) changes from a liquid state to a vapor or gas state.

Evaporation is great for separating a mixture (solution) of a soluble solid such a table salt and a solvent such as water.
The process involves heating the solution until the solvent evaporates (turns into a gas), leaving behind the solid residue.

Here is a simple example involving a mixture of salt and water.

To get the salt back from the saltwater, the solution is heated to a boiling point. As it boils, the water escapes as vapor (gas). After some time, all the water evaporates, leaving a layer of salt at the bottom of the beaker.