This post is helpful for beginners in Sitecore development. This tutorial helps creating pages in Sitecore from the scratch involving custom layouts, templates, renderings, content items with presentation details.
This post explains what templates and fields are in Sitecore and the differences between the Versioned, Shared and Unversioned fields in Sitecore. It also states the scope of each of these fields in different scenarios.
This post highlights the best practices to be followed for the visual studio sitecore solution which is used with Sitecore website folder. If you are looking for integration of a new visual studio solution with Sitecore then this post might help you - Integrating Visual Studio solution with Sitecore MVC - basic
Sitecore is a .NET application and adding any new functionalities to it requires adding of .NET components to the Sitecore instance. So it is required to create a Visual studio solution and move the changes from visual studio to Sitecore instance as and when required.