An explanation of vapor pressure

Vapor pressure is constant when there is an equilibrium of water molecules moving between the liquid phase and the gaseous phase, in a closed container.

The vapor pressure of a liquid is the point at which equilibrium pressure is reached, in a closed container, between molecules leaving the liquid and going into the gaseous phase and molecules leaving the gaseous phase and entering the liquid phase. Note the mention of a "closed container". In an open container the molecules in the gaseous phase will just fly off and an equilibrium would not be reached, as many fewer gaseous molecules would be re-entering the liquid phase. Also note that at equilibrium the movement of molecules between liquid and gas does not stop, but the number of molecules in the gaseous phase stays the same—there is always movement between phases. So, at equilibrium there is a certain concentration of molecules in the gaseous phase; the pressure the gas is exerting is the vapor pressure. As for vapor pressure being higher at higher temperatures, when the temperature of a liquid is raised, the added energy in the liquid gives the molecules more energy and they have greater ability to escape the liquid phase and go into the gaseous phase.

Turnip greens in a hurry

If you wanted to cook your turnip greens quicker you would want the water temperature to be higher. But, in an open container, water boils at 212°F (at sea level), and if you continue to heat the water you will release more molecules as water vapor but the temperature of the water won't go higher than 212°. Now, this assumes you live at sea level, since as the higher your kitchen is above sea level, the lower the air pressure pushing down on the water in the pot of turnip greens, and the lower the vapor pressure, and thus, the water will boil at a lower temperature. That is why it takes longer to cook food at higher altitudes.
The point is, in an open container once water reaches the boiling point it will not get hotter. You can use vapor pressure to "trick" your turnip greens, though, by using a closed container to cook in—known as a pressure cooker. Pressure cookers have lids that can be secured to the pot which prevents steam from escaping the pot, which raises the pressure of the vapor inside the container. There is a pressure-release valve on the top of the pot to prevent pressures from getting so high that the pot explodes (although there are many instances of the valve malfunctioning with the disastrous effect being a pot that literally explodes). We mentioned that with a higher vapor pressure higher water temperatures can be reached, meaning that in a pressure cooker the vapor pressure is much higher and thus, the water doesn't boil until it reaches a higher temperature, which cooks the food faster.