What is a plate
Plates are sections of the earths crust which floats on the mantle.
What is the lithosphere
The upper layer of the crust and the upper mantle
How do convection currents cause plate movement
The hot core heats the mantle and this causes convection currents.
As these currents reach the top of the mantle and spread out, they drag the plates slowly apart.
When they cool and begin to sink back towards the core they drag the plates closer to together.