Similarly to adding almost anything to your site, to add a gallery, you use the add element again. Each gallery you will see will be different from each other. From professional looking galleries to the less so professional. Wherever you choose to place a gallery on your site, always make sure the images are appropriate for the page or your website.
Once in the navigation, you can choose between many different styles of menus. Once you choose the navigation you would like, WIX will automatically include each of your pages within the navigation bar. To place on your page, just drag and drop. Once on your page, you can fix to the whichever size you would like. Big or small, it is up to you. Also remember to place within the header of the page, as the navigation will then show on each page of your site.