Nothing could be easier: once your collections are created, just go to the “Menus” section, then choose the part of your store where you want this collection to appear: top menu or bottom menu.
Next, you can either “add a menu,” and the collection will then appear at the very top of the store or at the bottom, next to your homepage for example.
You can then enter the name of your collection, followed by its URL. Here's what it should look like: https://nomdevotreboutique.tpopsite.com/accessoires
If you now want the collection to appear in a submenu, you'll need to click on the small button in front of the main menu:

By clicking on it, a submenu will magically appear, and you can fill in the required information: collection name and its URL.

Here is the result on your store: there are several possibilities, either the collection is visible in the main menu (bottom or top of the site), or it appears in a dropdown menu when you click on one of the main menus.
