Personalised menu in Goodspace

Hi, apologies in advance as I am a total neophyte.

I am working on updating a website that was initially created by another programmer using the Goodspace theme.

It has a main menu and some side menus in a left sidebar that allow navigation between sections of the same page. I have created a new menu and a new page. The page is titled ‘essays’ and the new menu contains all the titles of the different essays that are going on this page.

Problem is, when I go on the page’s settings and select the left sidebar layout, the new menu ‘essays’ doesn’t appear in the ‘choose left sidebar’ scroll down menu.

I understand I have to create a ‘personalised’ menu, but how do I do that? I tried adding a widget but I am under the impression that I have to modify the code…

http://www.mariellabettineschi.it/wp-admin/post.php?post=1744&action=edit

http://www.mariellabettineschi.it/wp-admin/nav-menus.php

Can anyone help, please?
Thanks!