  We describe astrophysical processes around a black hole keeping primarily the
physics of accretion in mind. In Section 1, we briefly discuss the formation,
evolution and detection of black holes. We also discuss the difference of flow
properties around a black hole and a Newtonian star. In Section 2, we present
past and present developments in the study of spherically accreting flows. We
study the properties of Bondi flow with and without radiative transfer. In the
presence of significant angular momentum, which is especially true in a binary
system, matter will be accreted as a thin Keplerian disk. In Section 3, we
discuss a large number of models of these disks including the more popular
standard disk model. We present magnetized disk models as well. Since the
angular momentum is high in these systems, rotational motion is the most
dominant component compared to the radial or the vertical velocity components.
In Section 4, we study thick disk models which are of low angular momentum but
still have no significant radial motion. The accretion rates could be very high
causing the flow to become radiation dominated and the disk to be geometrically
thick. For low accretion rates, ion pressure supported disks are formed. In
Section 5, we extensively discuss the properties of transonic flows which has
with sub-Keplerian angular momentum. In the absence of shock discontinuities,
these sub-Keplerian flows are basically advecting, similar to Bondi flows,
close to the black holes, though far away they match Keplerian or sub-Keplerian
disks. In presence of shocks, the post-shock flow becomes rotation dominated
similar to thick disks. In Section 6, we present results of important numerical
simulations of accretion flows. Significant results from the studies of
evolution of viscous transonic flows are reported. In Section 7, we discuss
some observational evidences of the black hole accretion. We also present a
detailed model of a generalized accretion disk and present its spectra and
compare with observations. In Section 8, we summarize the review and make
concluding remarks.
