How does vapor pressure affect the boiling point of a liquid?

Vapor pressure is the pressure exerted by a certain amount of gas in equilibrium with the liquid and solid phases of a substance, and is proportional to the amount of gas present.

There are 3 key ideas to understand here:

1) Boiling point is the temperature at which a substance changes from liquid to gas.

2) Molecules in a liquid sample will transition to a gas when their vapor pressure is equal to the surrounding .

3) The Vapor Pressure of the substance changes with temperature. (higher temperature, increase in VP)

When you put this all together, it means that there is a temperature that exists where the vapor pressure of a substance is equal to the surrounding atmospheric pressure... we call that temperature the boiling point.