Installing from composer is easy,

Create or edit a composer.json file in the root of your SilverStripe project, and make sure the following is present.

{
    "require": {
        "marketo/silverstripe-menumanager-squared": "~1.0.0"
    }
}

After completing this step, navigate in Terminal or similar to the SilverStripe root directory and run composer install or composer update marketo/silverstripe-menumanager-squared depending on whether or not you have composer already in use.

Add MenuSets to your yaml file with max depth.

The depth variable demarcates the allowed ChildItems of MenuItems of a particular MenuSet.

A MenuSet with depth 0 can only have MenuItems, a depth of 1 indicates that this MenuSet’s first MenuItems can have Child Items, a depth of 2 indicates that this MenuSet’s MenuItems can have Child Items that can have Child Items of their own etc.

MenuSet:
  default_sets:
    - Main
    - Main2
    - Footer
  Main:
    depth: 2
  Main2:
    depth: 1
  Footer:
    depth: 1

MenuSet depth defaults to 1.

Menu Manger Squared adds the following fields to MenuItem:

1. ChildItems
2. Image

Separators can be identified by the class MenuItem_Separator

<% loop $MenuSet('YourMenuName').MenuItems %>
    <a href="$Link" class="$LinkingMode">$MenuTitle</a>
    <ul>
        <% loop $ChildItems %>
            <% if $ClassName = 'MenuItem' %>
                <li>
                    <label>$MenuTitle</label>
                    $Image
                    <% loop $ChildItems %>
                        <p><a href="$Link" class="$LinkingMode">$MenuTitle</a></p>
                    <% end_loop %>
                </li>
            <% else_if $ClassName = 'MenuItem_Separator' %>
                <hr>
            <% end_if %>
        <% end_loop %>
    </ul>
<% end_loop %>