The same process is used for adding definitions of any type. You can select where to get the definition from using the following dialog...
Options
New - If available, this open will allow you to create a new definition from scratch.
Load - You can load a definition from file or the online library. For more options, click the drop arrow by the Browse button.
My Library - The new definition is created by copying one from the library. The library is a folder of building-block files, and is located in the DX Studio™ install directory, under the sub-folder 'library'. Any files of the appropriate type found in this folder will be listed here, and you can copy or remove your own files to/from this folder.