how can I use the preloader to load all assets before starting the composition

This part I understand:

<script>

    window.AdobeEdge= window.AdobeEdge||{};

    window.AdobeEdge.bootstrapLoading =true;</script>

<!--Adobe Edge Runtime--> <script type="text/javascript" charset="utf-8" src="project-name_edgePreload.js"></script>

This part I do not know how to use:

...

AdobeEdge.loadResources();

...

AdobeEdge.playWhenReady();