Like Weebly and WordPress, Wix has a sidebar with elements that add different functions to your site.
Adding a gallery:
Wix offers multiple choices and themes for gallery options.
Editing with HTML & CSS:
Editing with html and css is very similar to Weebly, where you select the html element and add html code.
Embedding works the same way it would for any other website platform. Wix offers an element box that is specifically for embedding.