Where will convection most likely occur?

Convection is the process of heat transfer through a liquid or gas, so it's like conduction except it is through a liquid or gas.

An easy example is to think of a pot of stew after it is done cooking and is removed from the stove. Denser material like beef, potatoes, vegetables, etc. will settle to the bottom of the pot. The broth remains on top and heat transfer occurs from the liquid first and faster than from the denser materials. The convection from the broth actually helps cool the denser material below.