  We discuss the prospects of using the redshifted 21~cm emission from neutral
hydrogen in the post-reionization epoch to study our universe. The main aim of
the article is to highlight the efforts of Indian scientists in this area with
the SKA in mind. It turns out that the intensity mapping surveys from SKA can
be instrumental in obtaining tighter constraints on the dark energy models.
Cross-correlation of the HI intensity maps with the Ly$\alpha$ forest data can
also be useful in measuring the BAO scale.
