We summarize the main results obtained by the joint effort of solar and stellar physicists in investigating solar and solar type activities in the low-mass main-sequence stars. We demonstrate the basic role of the magnetic field in this activity and the importance of its interaction with the convection and differential rotation of each star.
We compile the data obtained by ground-based optical, radio and space ohservations of these stars which provide some idea about the physical conditions in the stellar photospheres, chromospheres and coronae, their activity periodicities and relations of this activity to other stellar parameters. We discuss the possible depth of the
dynamo action in the Sun and stars in its relation to the convective zone. We present some results of the method of direct stellar magnetic field measurements in comparison with various indirect evidence of the action of stellar magnetic fields. We also show some observed differences both between the sun- and star-spots, and plages, and we bring information concerning stellar flares.
Finally, to compare the main behaviour of magnetic fields on the Sun and stars and the characteristics of the solar and stellar activities, we report some of the new observational results concerning the mutual relation of magnetic and other activities with torsional oscillations, various regularities in latitudinal and longitudinal background field concentration shifts, differential rotation and convection. We also summarize our current knowledge of active region energetics and developments.