Study of transient atmospheric events (TAE) is started by a new space instrument TUS, an imaging detector equipped with a large area mirror-concentrator (≈2 m²) and 256 photomultipliers in the focal plane. Its covering area in the atmosphere is 80 km×80 km. TUS was launched on 28 April 2016, and several hundred of TAE were measured during the first months of its flight. The detector has several modes of operation with different temporal resolution, which allow measuring TAE at various time scales. In comparison with earlier experiments, the instrument measures orders of magnitude less bright transient luminous events due to a large optical aperture. TUS has a spatial resolution (5 km from orbit height 500 km), which gives an opportunity for a reliable classification of TAE types basing on their temporal dynamics and spatial structure. Data on lightning are compared with data from ground-based networks and examples of TAE images are discussed.