If you use Android Studio to create an app using Android chart, you can download directly the jar containing all the classes and add it to your project. When the download is completed, you should add the library under libs folder so that I can be included automatically into your project. Now you are ready to use the lib!
When creating a charts in Android, you need usually a set of data that has to be drawn in the chart, in this case to have real values and to not re-invent the wheel we can suppose we get these values using WeatherLib so that we will plot the atmospheric parameters (like temperature, and pressure..).
There some basic concepts that stand behind this library and they are important so that you can use it:
Dataset (The set of data you have to draw in your chart)
The view (or the type of chart you want)
Renderer (It controls how the view is drawn, settings some parameters you can change the way the charts looks like. There are two types of renderer: one that controls the rendering of the dataset and another one that controls how the main chart aspects look like (i.e. axis, labels and so on)
Chart factory (combines the dataset and the renderers to create the charts. The chart can be created inside an Activity or the factory can return a View.)