You can create a user-defined function from a data development project in the Data Project Explorer, or you can create a user-defined function from a connection in the Database Explorer.
If you create a user-defined function from a data development project, you can use a wizard to guide you through the entire process, or you can simply specify a name and language for the user-defined function and then modify the source code in the routine editor. If you create a user-defined function from the Database Explorer, you can use the routine editor or the SQL editor.