USA Weather starts at Forecast window showing your current location forecast if it can be detected.
Here you can alternate between several information pages:
To alternate between pages press at bottom buttons or swipe right or left:
If your current location can't be detected or you want to search for another, use the Search action (the magnifier icon).
If you don't type anything in the search box you will see your nearest location and your favourite ones. And if you enter some letters or your zip code matching locations will appear.
To make a location favourite press on the star next to the location name in Current page.
To see your favourite locations press the Search action without typing anything.
To go to the maps use the top action bar menu (press where you see Forecast) and then select Maps.
You start at rain radar layer. You can change to other layers (visible satellite, precipitation amount, hazards,...) using the top right layers button:
Change layers button
In the bottom bar you have the navigation options. If you press on current showed time (TODAY 08:30 in the screenshot) you will see a list of all time steps.
You can also move in time with the Previous and Next actions and also animate with Play.
Don't forget to use the more actions or menu button if you don't see above actions or want to see some other ones not explained here.
Widgets are small info panels you can have in your home screen:
To create one in Android 4.0 or superior go to the Widgets tab next to the applications one.
In previous Android versions go to HOME window -> Menu button -> Widgets.
Once you are in widgets window look for one of the USA Weather ones and a configuration window will appear:
Here you can select to use always your current location (location change as you move) or enter one manually. You can also configure several widget parameters.
Now that you know the basics you can just use the application or check out the section that interests you.