I have an app that will be installed by the user from a public webserver (outside android market).
So I hosted the apk in webserver and instructed the users to type
Normally, you just link to the .apk file. When the user clicks on such a link, the .apk file is downloaded and the installation is automatically started (with a dialog like 'do you want to install this application').
So, just Download and install....
Important! This only works if your users allow installation from 'Unknown sources' in settings/security.