There are two ways how to to open, close and select objects. We can use either mouse or arrows. Up/down is used to go one object above/below current and right/left is used to open/close complex objects.
When an object is selected right mouse click opens a menu with operations we can perform on the object according to its type.
Mouse right click menu
We can add properties/objects using Insert key or clicking
Add button
button and delete properties/objects pressing Delete key or clicking
Delete button
button. Not always is adding and deleting possible.