It is simple with WordPress to create and modify a menu.
Go to the wordpress administration screen and search for Appearance
> Menus
.
Once accessed you have 4 types of objects to be included in your menu:
1) Pages

They are static custom pages created ad hoc.
2) Posts

Individual posts published on the site.
3) Custom links

Internal or external links to the site.
4) Categories

Perhaps the type of object that will be inserted most often, the category.
Categories can be created under Posts
> Categories
. You don’t need to order them in that section because when on the menu you can choose the order to be given to the menu items.