Cosmic dawn is one of the least-explored epochs in the history of the Universe illuminated by the very first stars and black holes. 21-cm radio signal produced by the intergalactic neutral hydrogen is tied to the intensity of radiation generated by these first sources of light. The signal can be used to constrain process of primordial star and black hole formation as well as reionization. In my talk I will discuss astrophysical processes that drive the signal. Pioneering radio experiments such as EDGES High-Band and SARASII deliver data which are capable to disfavor large sections of the high-redshift astrophysical parameter space. I will show the first observational constraints on reionization and cosmic dawn derived using the data of global 21-cm experiments at redshifts z~6-14. I will also discuss combined constraints with high-redshift quasars and Lyman Break Galaxies. Finally, I will comment on the claimed detection made with the EDGES Low-Band antenna at z~17.