Nuclear Readout Japan
Online help
When you first start the App you should see the screen as follows:

At the Top and the bottom there are sliders which you can activate to access differnt functions. The Top-Slider contains information on the current selected sensor and the current measured value in nG/h (nano Gray per Hour). A sensor is selected by touching on of the white circles on the map.

The bottom slider gives you access to the buttons for controlling the differnt layers on the map (e.G. power plants, stations...). The Button on the right switches GPS or Network-positioning On or Off:

In the screenshot above for example, all layers and functions except the weather warnings are switched on and appear colored. The weather warnings are switched off and therefore appear gray.

Weather warnings
When you hit the weather warning symbol (exclamation mark), the weather warnings screen appears. The weather warnings screen is described in detail here.
By hitting the menu key of your device you can access these functions: "Settings", "Overview", "Help" and "License":

"Settings" takes you to the settings screen which is described here. "Overview" centers the map in a way that you have an overview of the whole country. "License" shows you information about the license and finally "help" takes you to this page.
I hope i could help you a little in how to use the App.