Nima's interface is minimalist by design. It only shows what is needed, when you need it. The interface is divided into a few main panels.
On the far left, you have the Hierarchy Panel. All the stage objects, assets, controls, and animations that make up your character appear in the Hierarchy Panel.
Read more on the Hierarchy Panel page.
The Selection Panel is immediately to the right of the Hierarchy Panel. It lets you adjust the properties of the currently selected item. In Animate mode, you will only see properties that can be animated.
Read more on the Selection Panel page.
The Toolbar is on the far right. It displays the tools you have available to manipulate and create items on the stage. Note that these change based on whether you are in Setup or Animate mode.
Read more on the Toolbar page.
The Animation Panel appears when you switch to Animate mode. It displays a timeline and playback controls/options for the currently selected animation (notice the currently selected animation in the Hierarchy Panel in the image above).
Read more on the Animation Panel page.
The stage is where your character and animations are rendered.
Read more on the Stage page.