Sharepoint Hierarchy

Here is some links about sharepoint hierarchy.
Site Hierarchy
(1) Understanding the Microsoft Office SharePoint Server 2007 containment hierarchy to design efficient information architectures

(2) SharePoint Object Hierarchy: How it all fits together

(3) Server and Site Architecture: Object Model Overview

(4) The Services Hierarchy of Microsoft SharePoint Foundation

Directory Hierarchy
(1) Sharepoint 14 hive directory structure

(2) 14 hive and other SharePoint 2010 directories

(3) SharePoint - The 12 Hive

(4) SharePoint - Get to know the directory structure in the 12 Hive

(5) 12 Hive Folder Structure

What is Web Part?

Here is some links about Web part in SharePoint.
(1) Introduction to customizing pages by using Web Parts

(2) Introduction to Webparts in Sharepoint

(3) Source Code for the Built-in ASP.NET 2.0 Providers Now Available for Download

(4) SharePoint 2007 -- Built on ASP.NET 2.0

(5) Writing Custom Web Parts for SharePoint 2007 - ScottGu's Blog

(6) Working with Outlook Web Access Web Parts in SharePoint Server 2007

(7) Microsoft Office SharePoint Server (MOSS) for Developers, Introduction to Web Parts

(8) SharePoint for Developers