I have installed 2.3.1 and I do not see the editors like I see in the demo website where there are editors for left middle and right is there anything I am missing on my install.

This is the image of the admin on my install of silverstripe 2.3.1 that has only content editor not same as the demo that has left and right editors on the page

I'm not sure what the left and right areas are that you are referring to. It sounds like you just want to add another HTML editor field to page.

If you look at http://doc.silverstripe.com/doku.php?id=tutorial:2-extending-a-basic-site you can see how to do this. Look for the section explaining this code:

function getCMSFields() {
$fields = parent::getCMSFields();

$fields->addFieldToTab('Root.Content.Main', new CalendarDateField('Date'), 'Content');
$fields->addFieldToTab('Root.Content.Main', new TextField('Author'), 'Content');

return $fields;
}

But what you want is to add an HTMLEditorField: http://doc.silverstripe.com/doku.php?id=HTMLEditorfield

I have been investigating and think those extra editors in demo are the tree boxes on the home page on this page http://demo.silverstripe.com/
To get the same what files do I have to modify

Ok, I see what you mean. Yes, you need to write PHP code to add three more text editors on the Homepage class.

I've moved this away from install issues because it is not an install problem at all.