Another major difference between the James Webb Space Telescope and it's predecessor, is that while the Hubble could see in near ultra-violet, visible light, and near infra-red, the new telescope will focus solely on infra-red light. One reason for this is that objects with a high red-shift, which the telescope will be looking for, emit IR light (color-shift is essentially comparable to the Doppler effect, but with light, and help determine whether objects in space are coming or going). In addition, cold objects, such as planets, are more visible in the IR spectrum. Finally, infra-red is also difficult to observe from earth, and is thus more suitable for a space-based telescope.
A rendering of what the JWST will look like deployed
When completed, the James Webb will be launched into space by an Ariane 5 rocket, and will then be flown to the Earth-Sun L2 point, some 1.5 million km from Earth. The L2 point is known as a Lagrangian point, one of five in the earth-sun system, where an object can remain in orbit around the two bodies by their combined gravitational pulls. This site was chosen in favor of a closer orbit, because it keeps the telescope well clear of our planet, and any infra-red emissions it, just like any planet, will produce.
Ultimate, there are four goal for which NASA is putting down all this work and trouble to accomplish: First, the JWST means to look for light from the very first stars and galaxies formed after the big bang; galaxies and stars so distant that the light emitted from them left those stars and galaxies when the universe was an infant. The second goal is to study the creation and life-cycle of galaxies. The telescope also means to study the formation of stars and planetary systems. Finally, and perhaps most excitingly, the James Webb will be finding new planetary systems and the studying the origins of life; the James Webb has an onboard infrared spectrograph, and theoretically, if it can capture light streamed through the atmosphere of an alien planet, it can analyze the light to separate which chemical compounds exist in the atmosphere, and possibly detect signs of life.
Whatever the end result may be, the Hubble never ceased to amaze, and the JWST probably won't either; 2018 will no doubt be a very interesting year.