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Hydrogen is the most abundant element in the Universe and it exists in different forms and scales. In the galaxies, neutral cold atomic hydrogen acts as a fuel reservoir for the star-formation activity and hence it is important to study this phase of gas in different types of galaxies. In the radio bands, it can be traced using a 21-cm spectral line through absorption or emission. In this presentation, I will talk about 21-cm absorption in the host galaxies of radio AGNs and 21-cm emission in the blue compact dwarf galaxies. Radio AGNs through their feedback effects can significantly affect the star-formation process in the host galaxy and its evolution. 21-cm absorption can trace the cold gas in the interstellar medium and circumnuclear regions of the radio AGN hosts and can help understand the fueling and feedback processes. In this talk, I will briefly give an overview of HI absorption towards radio AGNs in the literature and present our recent work on HI absorption towards radio AGNs with Five-hundred-metre Aperture Spherical radio Telescope (FAST) where we discovered 5 new HI absorbers including 4 towards lowest radio luminosity radio sources in the redshift range 0.25-0.4. While radio AGNs are largely hosted in massive galaxies towards the end phase of galaxy evolution, dwarf galaxies occupy earlier stages of hierarchical galaxy formation models. Blue compact dwarf galaxies (BCDs) along with recently discovered Green Peas and Blueberry galaxies with low metallicity act as a local laboratory to understand the star-formation process in the early primordial Universe. In this talk, I will also present our work on HI in selected mid-infrared bright BCDs with the Arecibo telescope and GMRT where we find that these systems have very short depletion time scales of ~0.3 Gyr, and present some preliminary results on HI in Blueberry galaxies with FAST. I will conclude with a brief overview of the prospects of HI studies with Square Kilometre Array (SKA) pathfinders (uGMRT, FAST, ASKAP and MeerKAT) and SKA in future.