Due to a high-flux beam of pulsed neutrons, MLF at J-PARC is now opening a new world in biology and material science on functional structure and dynamics. A high-intensity small-angle neutron scattering spectrometer at MLF, called TAIKAN, can cover a very wide-range hierarchal structure that is essential for biological systems. Although small-angle scattering (SAS) using X-ray or neutron is a classical method, it is still intensively and widely used for structural characterization of various materials (ex. alloys, polymers, biological materials, liquids, etc.) since SAS enables to observe in-situ structures of materials under various conditions and to clarify hierarchal structures in the range from ~10-9 to ~10-6 m. In addition, the complementary usage of neutron and X-ray in SAS is also quite important, especially for clarifying structures of complex composed of different components such as biological supra-molecules. This review describes some basis of SAS principles and data analysis for studies of biological systems in solutions and intends to be a tutorial of beginners of SAS method.