Can you help?

I have come accross this udacity sunshine app. But they have provided almost 0 guideline on some of the important things. 

If you can please take some time and answer few of my questions. 

1. Why do we need a DB(table, content providers etc)
2. What is authenicator (cant we just use retrofit) what is this service folder for and its file. 
3. Why the location detection is not automatic?