The Layer tree represents the disposition of the components on your page.
To insert a new component on your page, click on the
+ button on the left sidebar and drag and drop one of the components in the list to the tree. You should immediately see it in the preview window. You can freely reposition a component in the tree.
Clicking on an element of the tree will reveal the
Property Sidebar on the right, and you will be able to access the context menu for that item. In this menu, you will find three buttons: