I was recently launch localhost server on my computer to create local website. If I create new link that add to top menu. The href value was http://localhost.com/something/something. Does this href value will change to my website name after I upload my website online ? http://mywebsite.com/something/something.
Sure it will change if it was created using the default WordPress menu. Wordpress stores a site url, which is usually the domain or exact path. On your localhost it will be something like localhost/site/about and the moment you deploy your site and update your database with your domain, www.yourdomain.co.za/ - that will automatically update the rest of the pages or links, e.g. www.yourdomain.co.za/about
So, to answer your question: Yes, but only if your used the WordPress menu