As per @joshua4 's suggestion, I’m posting this question so they can submit their solution to it here.
You do this in the exact same ways as with any other language.
[Tutorial] Introduction into object inspection with MRI
To expand on what Villeroy is saying…
https://forum.openoffice.org/en/forum/viewtopic.php?f=74&t=49294
http://www.openoffice.org/api/
then search under the Office API reference field.
This will add a sheet as the second sheet:
//Mini-dmonstration of how to add a sheet
// for Calc using LibreOffice implementation of Rhino
//Import the Uno runtime interfaces
importClass(Packages.com.sun.star.uno.UnoRuntime);
importClass(Packages.com.sun.star.uno.XInterface);
//Import the Uno Calc interfaces
importClass(Packages.com.sun.star.sheet.XSpreadsheetDocument);
importClass(Packages.com.sun.star.sheet.XSpreadsheets);
importClass(Packages.com.sun.star.container.XIndexAccess);
//Rhino seems to have these handled...
//importPackage(java.type);
//importClass(java.lang.Integer);
//Get sheets object
var polySheets = UnoRuntime.queryInterface(
XSpreadsheetDocument, XSCRIPTCONTEXT.getDocument()
).getSheets();
var xspreadsheetsSheets = UnoRuntime.queryInterface(XSpreadsheets, polySheets);
//Insert new sheet in position 2 (i.e. index 1)
xspreadsheetsSheets.insertNewByName("NewerSheet", 1); //Will throw if name is not unique
//End