This telescope element of JWST includes the optical components and science instruments. After testing, the telescope will be affixed to a sunshield to prevent thermal heating and a spacecraft bus that contains the propulsion and communication systems to complete JWST. Launch is scheduled for October 2018.
Building the telescope element of JWST has been a two-decade process involving the construction of new assembly and testing facilities required to build the telescope itself. A new composite material that retains its shape even at temperatures near absolute zero was developed for the frame of James Webb, and to remain precise in the harsh conditions of space, the mirror for JWST consists of 18 gold-plated beryllium segments.
One of the first things it will look at is the Alpha Centauri system, the closest stars to us, to search the planets orbiting there for water vapor.
NASA's Goddard Space Flight Center/Michael McClare has produced a video.
SOURCEs- NASA, Goddard, Youtube, Popular Mechanics