When you have your entity all set up with bodies, joints and such, it is time to test how it would look in the game. That's what the Entity Preview window is for. In this window you will be able to see how the entity would look ingame, meaning it will be physically simulated. In it you will also get to edit the entity's animations, if any. To start the preview, just press the “Toggle preview” button (the one with cogwheels) in lower toolbar.
The window behaves just like a regular viewport. You can move and orbit the camera around the model the same way. Added to this, you can use the mouse pointer to actually “pick” and drag physical objects in the scene.
The buttons below the previous ones work as follows:
Animation Editor pane
With this tool you will be able to add, delete and edit animations for the current entity.
Animation related controls
: The event will play the sound picked with the File control.
Transition list: Shows every transition defined for the current animation
Notes on the timeline workings: event markers will only be shown when the event tab is selected. The timeline will play transition previews and will show transition markers when a transition on the Transition tab is picked, otherwise the current animation will be played.