  The observed structures in the universe are thought to have arisen from
gravitational instability acting on small fluctuations generated in the early
universe. These spatial fluctuations are imprinted on the CMBR as angular
anisotropies. The physics which connects initial fluctuations in the early
universe to the observed anisotropies is fairly well understood, since for most
part it involves linear perturbation theory. This makes CMBR anisotropies one
of the cleanest probes of the initial fluctuations, various cosmological
parameters governing their evolution and also the geometry of the universe. We
review here in a fairly pedagogical manner the physics of the CMBR anisotropies
and explain the role they play in probing cosmological parameters, especially
in the light of the latest observations from the WMAP satellite.
