2 webpage on 1page?

If you are using PHP it's really quite simple

check to see if the $_GET variable exists and echo out content accordingly.

 

In blogspot you can hide it but someone clever will always be able to find it.
If you are serious about your content and your site you wouldn't be on blogspot anyway

You can use javascript to check the variables and then write content and hide the content in a js in dropbox and it would be hard to grab but not impossible.

 

I haven't played with templates in blogspot in years but whenever I review one it seems that people put the javascript in the page. Presumably you can also link to a file called mysecretstuff.js that you've saved in a public dropbox folder

In mysecretstuff.js you'd have

function getQueryVariable(variable) {
       var query = window.location.search.substring(1);
       var vars = query.split("&");
       for (var i=0;i<vars.length;i++) {
               var pair = vars[i].split("=");
               if(pair[0] == variable){
                  if (pair.length == 1) { return true; }
                  else { return pair[1];}
       }
       return(false);
}

function getSecretStuff(){
  var e = document.getElementById('secretspot');
  e.innerHTML = "What you want to hide";
}

function getPublicStuff(){
  var e = document.getElementById('secretspot');
  e.innerHTML = "What anyone can see";
}

if (getQueryVariable('view_hidden_html')) { getSecretStuff(); }
else { getPublicStuff(); }

Code (markup):