Convection is the transfer of heat in liquids and gases.
The hotter the liquid/gas the particles move faster and spread out. This means the gas/liquid becomes less dense.
The less dense gas/liquid rises and the more dense gas/liquid sinks.
Because the particles have to rise and fall for convection to occur it can only happen in liquids and gases, where the particles are free to move.
Real Life Example
A lava lamp - The light bulb heats the wax causing it to heat up and rise. The wax cools at the top and sinks again.
Conduction is how heat energy is transferred through solids when they are heated. Heat energy can also be passed from one solid to another by conduction.
Conductors are materials which transfer energy more easily. Insulators are materials which don't transfer heat as well. E.g. Galss and plastics.
As the conductor is heated the atoms gain more energy and vibrate more. This causes them to collide with other atoms transferring the heat energy.
Why are metals good conductors?
In a metal lattice electons from the outer shell are freed from their atoms. This causes those atoms to become positively charged ions. Heating the metal causes these ions bto vibrate more. This extra energy is transferred from hotter to colder parts of the metal by the free electrons colliding with other ions and transferring their energy.