These are the expanded lecture notes of the author's webinar series at the Gökova Geometry Topology Institute between the dates August 23 - August 26, 2021. The main goal of these lecture series was to familiarize the audience with some of the major developments in the theory algebraic group actions that took place in the last several decades. Most of the lectures were geared towards non-experts. While introducing some basic notions of Lie groups and algebraic groups in a down-to-earth manner, we tried to provide a short but self-contained overview of the classification of the reductive group actions of complexity \( 0 \).