There are many factors that determine how long a page takes to show up in a browser. When a page is requested by a browser, the server needs some time to compute the page contents (controller, model/database, view) and returns HTML to the browser. Besides network latency and throughput (which can be optimized by choosing a good hosting provider), there are several ways to speed up the page generation itself (like memoization, action/fragment/query-caching, using memcached, and so on).
But even after the HTML page itself has been transferred to the browser, the page is not necessarily ready to display yet. A page usually references more resources like stylesheets, javascripts and images that need to be requested and transferred. These are mostly static files (located in the public folder of a Rails application) and are directly served by the webserver without invoking the Rails application. So these files takes very little computation time on the server, but they still need some time and bandwith to transfer, which can be optimized.