Superfluid turbulence (ST), also known as quantum turbulence, is a tangle of quantized vortex lines in a superfluid. ST can be created in a number of ways: (i) as a result of non-equilibrium kinetics of Bose-Einstein condensation, in which case it is a manifestation of generic Kibble-Zurek mechanism, (ii) in the counter-flow of normal and superfluid components, (iii) as a result of macroscopic motion of a superfluid, in which case it can mimic (at large enough length scale) classical-fluid turbulence. We will make an introduction to the theory of relaxation kinetics of superfluid turbulence at T=0. The physics of zero-temperature limit is very rich and attractive in view of essentially conservative character of vortex dynamics. The theory will allow us to interpret recent intriguing experiments by A. Golov and collaborators.