The Element Tree is where the component of your composition will be. Note that on the contrary than on any other
compositing software, the first layer is on the bottom of the tree. And the background will be on the top of the tree.
Moving by Drag and drop
When doing a drag and drop on the Left the element will be attached to the parent of the layer (in the image to the compo)
and if it's on the Right it will be attached to the layer (in the image to the Feedback modifier)
To replace an Element by another:
1) drag and drop the new file onto the already existing element by keeping ALT down.
2) drag and drop the new file directly into the "file" parameter of the existing element.
3) select the existing element, go into the "File" editor on the bottom and change the file there by double clicking.
To duplicate an Element:
2) Ctrl+drag and drop.
To create a mask over an Element:
1) Ctrl+ drag and drop over a modifier (/!\ doing this manipulation on a modifier map will replace it)
Note that to create any element inside of the element tree, everything is accessible from the right click. Right clicking on the empty space on the bottom of the tree will result in creating an element on the top of the composition.
To create an element, you can also press CTRL+space to go into the instantiator and then type the name of the element or a preset (go check
Be fast, be free, fly like an eagle over the beaches of Normandy
) you want to create to instantiate it.