ИСТИНА

This invited lecture was presented for participance of the Summers school "Sun, space weather and space climate" in the framework of this conference: The Abstract: Several observational projects fulfilled during past 25 years allow us to trace changes of activity of sun-like stars throughout all stages of their lives from an epoch of star formation to the age when the cycle becomes regular, and up to the present. We will consider distinctions between saturated activity intrinsic to the youngest fast rotating low-mass stars and solar-type activity typical for older Suns. We discuss frequency of superflares on the Sun and other stars, and a role of local and large-scale magnetic fields in formation of flares. All these points are important for understanding space factors affecting on physical conditions on the Earth and its geo- and biosphere.