Multiple Forms, One Project

Question

I would like to be able to click on a button on my main.html form in an Web App Google Apps Script to go to another html page.

But how do I implement this with the doGet() function:

function doGet() {
  var clientss = SpreadsheetApp.openByUrl("https://docs.google.com/spreadsheets/d/P4ZgBlgYZYHH8Ga3HHs/edit#gid=0");
  var clientws=clientss.getSheetByName("Clients");
  var htpage=HtmlService.createTemplateFromFile("NewJob");
  var clientlist = clientws.getRange(2,1,clientws.getRange("A2").getDataRegion().getLastRow(),5).getValues();
  htpage.clientlist=clientlist.map(function(r) {return r[0];});
  return htpage.evaluate(); 
}