To get short-range interaction from long-range interaction Interactions in Condensed matter systems are almost exclusively the electromagnetic interactions which are long-range. But it often gives rise to short-range interactions in systems e.g., exchange interaction, interaction between electrons of a cooper pair etc. How is it possible that in reality the interactions which are long-range become short-range? Is there always some screening effect going on?
 A: Your are correct in saying that screening is a major reason for long-range Coulomb interaction effects to appear as short-range interactions, for example, in metals. The intuitive picture is that an individual electron is surrounded by a 'screening cloud' formed by the surrounding electron gas. This collective object is called a quasi-electron. These individual quasi-electrons do still have a residual interaction with each other, but this interaction is now short-range, and much weaker. The interactions of these quasi-particles are described in Fermi-liquid theory.
We know by experience that this picture works extremely well in metals; in fact, in many cases it is completely sufficient to treat the electrons in a metal as non-interacting.
Added note: Electrons in the conduction band are neutralized by a background of positive charges of the ion cores. Reducing the electron density locally therefore leads to the appearance of a net local positive charge, which can screen the Coulomb potential of an individual electron. This is the mechanism how the above mentioned screening actually works.
