Select View/Expression browser… from the main menu.
Right click on the library tree and select New library…
Now fill in the library information. The mandatory items are Library name and File name. Remember to place the file in your library directory. It's the same directory, where the “Basic geometrical formulas” library is located. For instance:
If you try to place the file in a different directory, Kalkules will show a warning.
You can fill in additional information like the library version, your name, website and email. You should also enter a short library description where you describe what kind of expressions the library contains.
After pressing ok, the new library is created.
Your new library doesn't contain any expressions yet. To fix this, read the article on how to add expressions into a library.
If you think that you have created an expression library, which can be useful for other people too, you should consider sharing it.