All the menus applied in the site are created in Dashboard -> Appearance -> Menu. WordPress manual: https://codex.wordpress.org/WordPress_Menu_User_Guide provides detailed instructions on creating/editing/saving menus.
There are two menu locations: the Main menu and the Mobile menu. One and the same menu maybe both: Main and Mobile. In addition, the WoodMart theme provides various options to display menus in any place on the site, it is possible to create as many menus as required, more detailed descriptions of the menus options are provided here: Adding a menu to the site.
WoodMart Theme extends the default WordPress menu by means of megamenu blocks. Megamenu blocks are WP Bakery page builder or Elementor templates, allowing to add of any element or widget: text, images, product grid, and other static elements. In most cases, the demo uses the Extra menu element/widget to make the sub-menu better arranged and looking nicer.
In order to create a megamenu it is necessary to create HTML block separately for each menu item in Dashboard -> HTML blocks - > Add new.
As soon as Megamenu blocks are ready, they may be added to menu items in Appearance -> Menu -> Select menu -> enter menu item -> HTML Block dropdown in the Custom fields [for theme] which appear only after the menu has been saved. First of all, it is necessary to set “Full-width” or “Set-size” in the Design option to make the HTML Block dropdown available.
Custom fields [for theme] in menu item: