@tushaar_srivastava This is what I understand about this API. Since there is not much documentation on how the API works and what each method actually does, I did some research. So basically the api helps to resolve your templates , structure node. Lets take an example of the WKND pages ( the sample project )
So lets say I have a page best-tacos-in-the-city.html This page is defined using article-page-template . Now for the article page template , you have a structure node , where the structure of your template is defined and the node structure for the same would be as below
TemplatedContainer API helps you to fetch these structure nodes or to check if the template has a structured content and its inherited methods from WCMPojo helps with a lot of other page and resource methods. Please check https://helpx.adobe.com/experience-manager/6-5/sites/developing/using/reference-materials/javadoc/co...
Coming back to the structuredResource ,
<sly data-sly-use.templatedContainer="com.day.cq.wcm.foundation.TemplatedContainer"
data-sly-list.child="${templatedContainer.structureResources}">
If you try to print and check ${child.path} , you can see that it resolves to the structure content node, in this case /conf/wknd/settings/wcm/templates/article-page-template/structure/jcr:content/root

In line 18 of the above body.html , when the child.path is included as a resource , you are actually including the "/conf/wknd/settings/wcm/templates/article-page-template/structure/jcr:content/root" node as a resource and that way all the below resources of the root node will get included to your page.
Hope this helps. Let me know if you have any more questions.
Thanks
Veena