It is possible to include WordPress navigation menu links to other sites. This is commonly achieved via two different methods.
Custom Nav Menu
Most themes allow you to create a custom navigation menu. Within that functionality is the ability to create a menu item that actually links to a url. That url can point to somewhere within the current website or to a completely different website.
Page Links To
A plugin called “Page Links To” is available. If you install this plugin, a field appears within the settings of each page that allows you to insert a url. Essentially, you are creating a fake page since the page exists but when people try to view it, they are actually redirected to the specified url. Note that if you use custom nav menus, you must include this page in the nav menu in order for it to appear.
Evaluating the Options
Custom Nav Menu vs. Page Links To
Both of the options above achieve the same goal of creating an item in your navigation menu that links to a particular url. However, you should be aware of the impact that these may have on your site’s Search Engine Optimization (SEO). When you use the Page Links To plug-in, you are creating a page within your site. If you have an XML sitemap function and set it to include your pages, then this “fake” page will be included in the sitemap. This often generates an error in Google Webmaster Tools since sitemaps are supposed to detail pages and content within your website and not point to another site.
To avoid SEO problems, use the Custom Nav Menu to insert WordPress navigation menu links to other sites. Nav menus are not included in sitemaps and will not cause an error in webmaster tools. Using this method also avoids installation of the Page Links To plugin. Whenever possible, it is a good idea to minimize the number of plugins that you use since they require updating and may conflict with other plugins.