  In this review article, we briefly outline our current understanding of the
physics associated with the HI 21-cm signal from cosmic dawn. We discuss
different phases of cosmic dawn as the ambient gas and the background
radiations evolve with the redshift. We address the consequences of several
possible heating sources and radiation background on the global 21-cm signal.
We further review our present perspective of other important aspects of the HI
21-cm signal such as the power spectrum and imaging. Finally, we highlight the
future key measurements of the Square Kilometre Array and other
ongoing/upcoming experiments that will enlighten our understanding of the early
Universe.
