If you don't see the edit icon, you should first go to sites.google.com, access the MXP site from there, and then return to your project page.
Google Sites does not have a built-in special character menu. In order to type a special character, you either need to write that character's ASCII code in the HTML code of your page or copy and paste the character from another location. Here is a convenient website for copying characters: http://greek.typeit.org.