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Heat is a form of energy.  It is disordered energy.  Work is the conversion of one form of energy into another form.
Can we do work with heat?  Can we convert it into another form of energy? 

is the study of the way that one does work with heat.
A very simple device that can convert heat into potential energy is a rubber band.  Unlike most other substances, rubber contracts when heated.  We can therefore lift an object by heating a rubber band.  Heat is converted into gravitational potential energy.

A simple rubber band can be the heart of an engine converting heat into electrical energy.  We can use heat to make the rubber band contract.  It then can lift water, converting heat into gravitational potential energy.  This gravitational potential energy of the water can be converted into electrical energy with the help of a turbine generator.  After the load had been lifted, we let the rubber band cool down.  It then has the same internal energy it had before we started the process.  We can repeat this process over and over again.  This certainly is a very inefficient engine.  It wastes a large amount of heat.  Can we make the process of converting heat into other forms of energy more efficient?

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Video:  A rubber band heat engine

Video:  Longer video clip with explanation