Question

Anyone know how to generally find the energy released in a fission/fusion reaction?

Answer 1

And what the difference between the two is?

Answer 2

Nuclear Fission and Nuclear Fusion are reactions involving the nucleus of Elements.
In nuclear fission- a the nucleus of a radioactive element ,say uranium235, is split by a high energy neutron to produce Krypton 92, Barium 141 , 3 neutrons and heat energy. these 3 neutrons further acts on multiple U235, to continue the reaction chain .The heat energy produced is utilized for generating electricity and other purposes. http://en.wikipedia.org/wiki/Nuclear_fission

In fusion reaction - multiple nuclei are collided to produce a heavy nucleus, neutron and heat energy. example-colliding isotopes of Hydrogen (deuterium & tritium) ,produces helium and heat energy. Fusion reaction takes place in stars.
http://en.wikipedia.org/wiki/Nuclear_fusion
energy calculation is based on mass -energy equation.....it is described in wiki pages