The concepts and Idea depends on what kind of web application are you trying to create.
If you are trying to create a blogging application, then you need a post detail page, archive page and few other pages which might be available in all other blogging software. Similarly, if it is a Inventory there will be different ideas.
I suggest you to try the Open Source CMS based on your requirement, Blogging, Ecommerce etc.
As our website name suggest, we have expert community of Microsoft.NET technologies but might not be help in PHP more.
All the Best.
Glad to be,
Editor - DNS Forums