Let’s say you have a website and a Windows Store app. If a user on Windows 8 navigates to the website and never installed the app, you can provide an easy way to point out the existence of the app in the Windows Store. Or if the user already installed the app, direct the user to the app, even in a specific section of the app.
Internet Explorer in Windows supports this scenario in the bottom app bar. It looks something like this:
If the app is NOT installed. If the app is installed.
To accomplish this, some meta tags must be added to one or more webpages on your website. By using these meta tags you can direct to the app, and even add parameters that the app can use to show specific content. This is not an automated process, the app has to process the parameters and navigate to the appropriate page and content.
More information on this can be found in an article on MSDN describing the meta tags.
The app bar or the menu as shown above are not opened automatically by IE. So it might be a good idea to also add visual clues on the page to direct users to the app.