Presentation covering basics of Reactive Programming, RxJava and RxAndroid prepared for GDG DevFest 2015 in Warsaw, Poland (http://devfest.pl). It was also presented during Gliwice Software Barcamp in January 2016 and Silesian Java Users Group (SJUG) meeting in Katowice in February 2016. Source code of the sample Android app shown and partially coded during the presentation is available at: https://github.com/pwittchen/guitar-browser