function onOpen() {
  var ui = SpreadsheetApp.getUi();
  ui.createMenu('Scripts')
    .addItem('Open Create', 'openCreate')
    .addItem('Open Perform', 'openPerform')
    .addItem('Open Catalog', 'openCatalog')
    .addToUi();
}
function openCreate() {
  var ss = SpreadsheetApp.openById("create ID goes here");
}
function openPerform() {
  var ss = SpreadsheetApp.openById("perform ID goes here");
}
function openCatalog() {
  var ss = SpreadsheetApp.openById("catalog ID goes here");
}

function onOpen() {
  var ui = SpreadsheetApp.getUi();
  ui.createMenu('Custom Menu')
      .addItem('Website', 'openSite')
      .addToUi();
}
function openSite() {
  var selection = SpreadsheetApp.getActiveSheet();
  var html = "<a href='url'; target='_blank'>Open Site</a>";
  var userInterface = HtmlService.createHtmlOutput(html);
  SpreadsheetApp.getUi().showModalDialog(userInterface, 'Open Google Site');
  }