The easiest way is to use the color picker. There are many ways to set the scrambled cube. There are two unfolded views which show each faces which helps setting up the scrambled configuration.
Rotate the cube with the arrows or swiping the screen.
The default 3D view can be customized, setting transparent front faces or you can lift the hidden faces. Start by selecting the most suitable view for you with the little tabs above the cube. For slower computers the program automatically reduces the computing performance to return a little longer solution. The app is using the open-source Kociemba algorithm to find the solution in 20 steps for any valid scramble. Hit the Scramble button and try to figure out the solution yourself rotating the faces with the buttons or with your keyboard. Use this application to play with the Rubik's Cube online.