Toolbox Integration using DTE

I am trying to integrate a customized control using DTE via steps:

• Check if an instance of Visual Studio is not running. If not, continue.
• Retrieve an EnvDTE.DTE object corresponding to the version of Visual Studio we want to integrate with.
• Create a "dummy" project using the DTE object
• Obtain Toolbox window and ToolBox object from it.
• Find or create ToolBoxTab object.
• Add item in the Toolbox tab (ToolBoxTab.ToolBoxItems.Add).
• Wait until current instance of Visual Studio stops running.

The 6th step "add new item under the Toolbox tab" is coded via "ToolBoxItems.Add" method.

Please help me in understanding what "ToolBoxItems.Add" method does internally.

Thanks