  We present an overview of the theory of high-redshift star and X-ray source
formation, and how they affect the 21-cm background. Primary focus is given to
Lyman alpha pumping and X-ray heating mechanisms at cosmic dawn, opening a new
observational window for high-redshift astrophysics by generating sizable
fluctuations in the 21-cm background. We describe observational prospects for
power spectrum analysis and 3D tomography (imaging) of the signature of these
early astrophysical sources by SKA1-LOW and SKA2.
