Reference numbers:
One(1) - Controls buttons. There are some fixed directions, as well as a switcher for free rotation/movement.
It's a default view for the 3d viewer.
Two(2) - Actions menu with different options like select part or tools with the measurement. This is the main menu with basic actions.
Three(3) - Assembly/Project view. Allows to switch the view and check the role of the assembly within the whole project.
Let's learn more about those features.