In this study, the geomagnetic storm that occurred October 6-10, 2015 was examined in detail. During the main phase of this storm, two large decreases in the disturbance storm time (Dst) index were observed, and this storm was classified as a two-step storm according to literature. In addition, the strong thermal emission velocity enhancement (STEVE) event that occurred in the main phase of the storm was documented with photographs taken by citizen scientists. The storm of October 7, 2015, which exhibits high-intensity, long-duration, continuous AE activity (HILDCAA), is one of the strongest storms of the 24th solar cycle. During this geomagnetic storm, changes in Dst index, interplanetary magnetic field (IMF) Bz, flow velocity, proton density, solar wind pressure, epsilon parameters were examined and the physical mechanism in the storm process was discussed. It was also analyzed in comparison with the 8 March 2008 and 25 July 2016 and 8 September 2017 geomagnetic storms. This research will contribute to a better understanding of the phenomena caused by solar wind.