Boiling and Evaporation

When a liquid is exposed to heat, the particles in that liquid once again break free from each other (just like a solid). The liquid then turns into a gas.

Take water, for example. Water is a liquid as it has no definite shape, a definite volume, it cannot be compressed and it can flow.
When water comes in contact with heat, the particles seperate even more, causing the water to evaporate (meaning it changes into a gas).
So, we turn a liquid into gas by boiling and evaporating.

Water evaporating from from a lake