The word strain means stretched. Strain energy can be stored in stretched springs and rubbers etc.
In any object the atoms are held together by forces, that are called bonds.
In some materials such as fuels and explosives these bond are found to be shorter or longer.
This store energy can be released by breaking up these bonds.
The energy in a nucleus of an atom is stored in strong bond between the particles of nucleus.
This energy can be released by splitting the nucleus into two small nuclei. This is done in nuclear power stations.
This is continued within an object and makes the difference between the object being hot or cold. Hot object has more internal energy.
Electrical currents carry electrical energy from one place to another.
It can be turned into kinetic internal energy in heaters / resistors etc.
Light carries energy as it travels.
This will be turned into internal energy if it strikes most objects.
It can also be used to generate electrical energy.
These carry a very small amount of energy from the source of noise.