Drag & Drop: Grab props from the left menu onto the stage.
Select: Click a placed prop to select it.
Move Object: Left click and drag a placed prop.
Rotate Object: Right click a placed prop to rotate 45°.
Lock Object: Double-click a placed prop to lock/unlock it.
Delete Object: Drag a placed prop onto the Trash icon at the bottom.
Camera: Use bottom-right arrows to pan. Scroll to zoom. Drag empty space to orbit.
Windows/Linux: use Ctrl instead of ⌘.