butch has basically covered it and has explained it well . I would add that energy transfer can occur at any frequency per se . Microwaves heat up water at around 2.5Ghz . All it needs is for the molecules or atoms to have a corresponding resonant frequency . This principle of resonance is very important . It basically is the connection between transfer of energy via oscillating forces - eg. EM fields - and atomic level movements . The heat we feel is atomic level movements where the atoms and molecules are restricted in their movements by atomic level forces - the hotter it is the more they jiggle .

Energy is the 'energy state' of the system - of the physical item in question . Energy itself cannot be bottled - it is essentially a construct . Heat is a form of energy but is no different than other such forms as it is just in terms of movement of the atoms and molecules . IR is not hot , however it can be converted into heat when it strikes an object due to resonance . Energy can be stored by imparting movement and by adding potential ( often the same thing ) . Potential is the level of force that can be exerted . An electron , for example , can be promoted into a higher shell , hence potential .