One of the most important aspects to a website is it's navigation, also called menus, these are how customers find products and information about your business.
In a typical website there are a few different kinds of menus.
The main menu is called the main menu because it's the first menu your customers will see. This is one of the most important areas on your entire website. Outside of search this is how most customers will navigate your website and find what they're looking for. It's important to include and prioritize any pages or information that are important to your business and customers. Is there a product or type of product that your store focuses on or sells well? Think about making that an important part of the main menu. Are there services that you offer or is there other information that could better tell the story of your business? Include those pages with informative titles and links.
A mega menu is just a variation of the main menu, instead of simple dropdowns it uses more content and imagery to make your website's navigation stand out.
Another variation of the main menu is your mobile menu. It's important for your site to be set up for all types of customers and their devices. Mobile is becoming a huge portion of traffic and your website comes equipped with a mobile friendly/optimized menu to better serve customers on the go.
A footer menu is another important menu on the site, different from the main menu, the footer menu is usually found at the bottom of every page. Because we only have so much room to work with in the main menu, the footer is a great area to add any other important links or information.