By default, the Start Screen only shows pinned applications. In order to see all applications, there's no direct way to do so. You can start typing something in the Start Screen, then clearing the search box, will provide you with access to the entire start menu, but it's not very convenient. An easier method would be to just have direct access to the "all apps" menu by using a shortcut (or tile if you will).

To do so, create a shortcut (or tile) pointing to:

%windir%\explorer.exe shell:::{2559a1f8-21d7-11d4-bdaf-00c04f60b9f0}

Place it anywhere you want. When hitting it, it will automatically bring you to the All apps menu. Pinning it to your task bar "sort" of simulates a start menu slash screen, without the need to install a third-party start menu replacer.

If you need an icon to go with your shortcut, you can use the one added here.