  We present a pedagogical introduction to the theoretical framework of the
Color Glass Condensate (CGC) and the McLerran-Venugopalan (MV) model. We
discuss the application of the MV model to describe the early-time dynamics of
the relativistic heavy-ion collision. Without longitudinal fluctuations the
classical time evolution maintains the boost invariance, while an instability
develops once fluctuations that break boost invariance are included. We show
that this "Glasma instability" enhances rapidity-dependent variations as long
as self-interactions among unstable modes stay weak and the system resides in
the linear regime. Eventually the amplitude of unstable modes becomes so large
that the growth of instability gets saturated. In this non-linear regime the
numerical simulations of the Glasma lead to turbulent energy flow from
low-frequency modes to higher-frequency modes, which results in a
characteristic power-law spectrum. The power found in numerical simulation of
the expanding Glasma system turns out to be consistent with Kolmogorov's -5/3
scaling.
