Convection is the transfer of heat through a fluid
Conduction is the heat or electric current from one substance to another
Radiation is energy that radiated or transmitted
Ex: Convection- A pot of water is being boiled- the heat is being transferred to to the water
Ex2: Conduction- I have a plate filled with hot food- the heat from the food is being transferred to the plate, making the plate hot as well.
Ex3: Radiation- There is a dog by the fire place, the dog is being warmed- the heat from the fire is being transferred over to the dog
Hope this will help you with your homework :)