There are basically three modes of heat transfer:
1. Conduction: Conduction is said to occur in solids mostly. In conduction, the solid gradually gets heated up until it reaches the temperature of the heating element.Holding a metal scale over a candle is a good example of conduction. In conduction, there is no net movement of the atoms of the metal. However, since the heat is also a form of energy, as you heat up the metal, the electrons on the metal surface start vibrating more and more violently. This results in each electron passing some of its energy to the adjacent atom and that electron starts vibrating and so on.
2. Convection: Convection is the mode of heating in liquids. Heating a pot of water on the stove is the best example of convection. Here, the heating effect is due to the actual movement of molecules. When a pot of water is held on the stove, the base of the pot becomes hot by conduction. Then, this heat is absorbed by the water molecules in contact with the surface of the pot and they then start moving about more randomly than they did before because of the increase in energy. This causes more water molecules to occupy the area they left at the base of the stove and then these get more energy. This process repeats until the water boils and gets converted into steam. Note that convection occurs by actual motion of the molecules.
3. Radiation: This form of heat transfer doesn't require any actual contact with the heat source. An example is, when we leave an iron nail in the sun, it gets heated up. But there is no contact between the sun and the nail. This is because of infra-red radiation, which is absorbed by the nail and it gets heated up. Radiation is also the prime cause for the green house effect and global warming.
Hope this was helpful