New textblock after click on button

using a c# script you would have to call something like this:

OnGUI()
{
    //check that the text has been added
    if(text != null)
    {
        //width and height of the text box pop-up
        int width = 60,
            height = 20;
        Vector2 boxPosition = new Vector2((Screen.width / 2) - (width / 2), (Screen.width / 2) - (width / 2)),
            boxSize = new Vector2(width, height);

        //draw the text on scrren
        GUI.Label(new Rect(boxPosition, boxSize), text);
    }
}

I've simplified it so that it is easy to read but you could make it way more compact once you have it working