Question:What is Convection?
Consider the pattern of movement of the water in this beaker.
When a fluid becomes warmer it expands and its density decreases.
When anything is less dense than it's surroundings it will rise (or float) due to the buoyancy force (upthrust).
The rising fluid pushes colder fluid out of the way and causes a circulating movement of the fluid.
This is called a Convection Current.