In simple terms, a supernova is a very violent and powerful explosion of a star which release enormous amounts of energy. If such an explosion would occur within 100-200 lightyears from the Earth, it would mean the end of our planet, but luckily this supernova went off at a distance of approximately 23 million lightyear away. Even if this is far away, it is close on an astronomical scale and a rare opportunity to study a supernova in our galactic neighbourhood.
The supernova was discovered on August 24 by the Palomar Transient Factory, probably just hours after the onset, and is brightening rapidly. When it was discovered the magnitude was 17.2 and might reach 11th magnitude. The supernova is designated SN2011fe and is a Type-Ia supernova.
Unfortunately, the skies here in the North are still too bright for any visual observations, but hopefully it will be possible to glimpse this rare sight later during the autumn. Observers further south should make the most of the following nights however, while the Moon is new and out of the way.
Finding the location of the supernova is relatively easy, but seeing the supernova itself requires a telescope. It is located in the constellation "The Big Dipper" or Ursa major in the beautiful edge-on spiral galaxy M101 that can be found just north of the last two stars in the Big Dippers handle. The Galaxy itself can be seen in modest equipment, so unless you have a telescope at hand, long exposure photography will be needed to pick up the light.
Detailed finder chart: http://www.astro.caltech.edu/ptf/11kyl_finder.png
Below is a picture of the Galaxy (M101) taken with a normal DSLR and a 300mm lens.