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Globular clusters (GCs) are the oldest stellar systems in the universe, even older than their parent galaxies. Studying them is of interest since they carry information on the early stages of the formation of the Galaxy. Two colour time-series photometry of GCs and proper motion analysis enable us to build accurate Colour- Magnitude diagrams and conjecture the structure and evolutionary time-scale of low- mass post-RGB stars. Pulsating stars are accurate indicators of mean cluster metallicity and distance. We have been studying the variable star populations contained in a sample of nearly 35 Galactic GCs for more than two decades, in collaboration with astronomers at the Indian Institute of Astrophysics. In this talk, I will briefly describe our approach strategies to the understanding of GC and the structure of the Horizontal Branch, and comment on how we pass from the counting of photons at the telescope, to the determination of physical parameters of astrophysical interest.