To understand most essential Astophysical processes, e.g. star formation, acceleration and propagation of cosmic rays, one must understand properties of MHD fluid. Those fluids are turbulent and their properties are very different from those of laminar fluids that the theory usually deals with. I shall discuss what is known about turbulent fluids and further discuss how to test the theory with the spectral line observations. In particular, I shall discuss the techniques that make use of observations to determine the 3D velocity statistics, e.g. correlation functions of velocity fluctuations, spectra etc. The most promising of those are the Velocity-Channel Analysis (VCA) and its offspring Velocity Coordinate Spectrum (VCS) that are based on the analytical description of the intensity fluctuations in the Position-Position-Velocity (PPV) data cubes. Those cubes are available from observations. I shall show that a great advantage of VCS is that it does not necessary require good spatial resolution. As the result an important insight is possible into turbulence within supernovae remnants, external galaxies, distant molecular clouds and star-forming regions.