Work in progress
First of all, you have to understand that in Snap! there are menus and menu items.
A menu is a collection of menu items. The menu itself is a block that can be shown somewhere on your page. That block shows a title (the name of the menu) and links (the menu items.) However, by default blocks are marked as "Disabled".
To move a block from the Disabled section to another section, click on the Admin tab, then the Blocks icon. Here you see the complete list of blocks including your new menu. Click on the cross (+) and drag the block to another section1.