In this thesis React library was presented. React is free to use and open-source library written in JavaScript programming language. In the first chapter, the main concepts of React were described. The chapter starts by installation of React and the creation of first application using the npm package createreact-app was explained. The main topic of the chapter are React components: independent, reusable building blocks. We also explain the way that React uses them to render and compose user interface. Its lifecycle methods were described, as well as properties, and the internal state of React components, along with its use for establishing communication of multiple components. At the end of the chapter, it was shown how React manages events, as well as hooks, functions that were recently added to React which made application development in React much easier. In chapter two, several external packages were explained which are typically used within most React applications. Those packages are react-router-dom, reactstrap and axios. In chapter three, implementation of a more complex web-application was described. Its purpose is to manage development of agile projects. It was explained how to use the application and its features. Also, concepts from chapter one are demonstrated in practice.