The width of your screen is too small and so you are not able to work with the map properly! Please, try to use the landscape mode of your device or use the device with the screen of at least 800px wide.
Buttons at the top-right corner of the map window allow you to zoom in/zoom out (+ and - buttons) and zoom to default overview (home button).
You can also easily change the base map by clicking on the icon at the bottom-right corner of the map window.
You can fold in/fold out the layer menu sections in control panel on the right side of the screen to explore all the thematic layers. You can also show/hide the layers easily. The legend for each layer is placed in control panel, below the layer label. Some layers have a common legend.
Moreover, it is possible to adjust the opacity of the current (last added). The default opacity is set to 60 %. Use the slider at the top-right corner of the map window to set the opacity according to your preferences.