Create a Visual Studio project (this should generally be done only once for each instance of Sitecore). 

To create the project:

1. Open Visual Studio .NET.
2. From the File menu select New Project.
3. Select the language you would like to use (Sitecore internally uses C# exclusively).
4. Select New Project in Existing Folder.
   
   
   
5. Enter a name for your project.  Names should not begin with numbers or contain special characters. 
6. Enter the address of the website hosting the project, typically http://localhost in development.
   
   
   
7. In Solution Explorer, press the Show All Files button.
   
   
   
8. Right-click on References and choose Add Reference.
   
   
   
9. Browse to the /bin/ folder of the project and select Sitecore.Kernel.
   
   
   
10. Right-click on /web.config and select Include In Project.
    
    
    
11. Right-click on the /xsl/ directory and select Include in Project.
12. Open the /layouts/ directory, right-click on each Layout or Sublayout and choose Include in Project. 
    
    
    
    
    
    Layouts typically do not contain code-behind; Sublayouts commonly contain code-behind.  To be prompted to create a code behind, exclude a file from the project temporarily, then add it again.
    
13. Optionally, open the /sitecore modules/ directory in Windows Explorer and create one or more folders as needed.  Return to Visual Studio, refresh Solution Explorer and include these directories in the project.
14. Right-click on the name of the project in Solution Explorer and choose Properties. 
    
    
    
    Set Assembly Name and Default Namespace.