A pulse jet is an incredibly simple kind of jet engine, usually with no moving parts. They were used on the V1 flying bomb in WWII. Wikipedia probably explains it better than I can http://en.wikipedia.org/wiki/Pulse_jet_engine . The version in this video is a valveless pulsejet.

Basically, he put the combustion chamber of the pulse jet in a tea kettle, so instead of just glowing red hot when it's running, it heats water. Also, it's awesome.

A pulse jet is basically the predecessor to jet engines as we usually think of them, but they work more like the internal combustion engines we have in cars. They are basically combustion Chambers that are set up to emit the exhaust in one direction for thrust and reset for the next explosion.

The rapid fire explosions create a buzzing noise, and a decent amount of heat.

He's using the waste heat from an esoteric jet engine design to warm up his tea. Because he can.