Much like our home planet, our home Galaxy – Milky Way – also hosts several rivers. But these rivers are made of stars, and are known as “streams of stars”. Stellar streams are pristine structures that have been continuously orbiting our Galaxy for billions of years. Recently, they have sparked tremendous amount of interest among the community because of the potential scientific merits they hold for various cosmic studies.  The attempt of this lecture is to demonstrate how astrophysicists (like myself) turn such star structures into a tool to probe various cosmic problems, in particular to understand the nature of dark matter.