Create .dll in C# to access into my any project

You can't - you have to add a reference to an DLL you application references, including System ones. When you create a project in VS, these are added for you - look under References in your Project in the Solution Explorer pane.

You can add a reference to this list when you create a new project: http://stackoverflow.com/questions/9272239/how-to-add-custom-libraries-to-default-solution-template[^] and add the appropriate using statements by defualt by editing the existing project templates: Adding your items to Visual Studio default files[^]

Hi,

Use Gacutil.exe[^]

gacutil /i dllpath.dll

At the Wikipedia page, you'll find the requirements for assemblies residing in the GAC:

Global Assembly Cache:[^]:

Requirements

Assemblies residing in the GAC must adhere to a specific versioning scheme which allows for side-by-side execution of different code versions. Specifically, such assemblies must be strongly named.

But, as the others pointed out, you still have to add a reference to your assembly.