There are two variants to add a new element to your design:
To add a new element:
This way allows to add a new element by using the navigation buttons of Components tree.
To add a new element of the same nesting level as the currently selected one - click the button.
To add a new element of the lower nesting level as the currently selected one (to nest an element) - click.
There is the only way to delete an existed element. It consists in the following: