If you swipe up on the screen the menu bar at the bottom will appear (swipe down to hide again). Swipe left to right on that menu bar to change selection options.
You should get to a section with a square in the bottom right, an upwards pointing arrow and a diagonally pointing arrow. By clicking on the square you can enter settings. If you click the up arrow you can add icons (there are options for more icons and widgets at the top).
To move an icon hold it for a moment and then you should be able to move it. If you drag the icon to the 'x' at the bottom of the screen the icon will be deleted (you can put it back again).