Go to Apperance >Menu and Create a new menu. Give your menu a name and click the button to create menu. To add menu items, simply select options in the left side column by checking the box for pages, portfolio items,  categories, tags etc that you want to include and then click the Add to menu button. If You want to create a submenu. >>Next Step

You can create some simple mega menus with 1,2,3,4,5 or 6 columns by simply adding a couple classes to your parent menu item.First, create your menu. Then add the classname “megamenu” in the CSS Classes box for the parent item you want to have a mega menu dropdown on. Also add the classname “col-3” where 3 can be exchanged for 1,2,4,5 or 6 based