Clearly identify the release that these instructions apply to. Otherwise, if users have multiple versions of your product, it is possible that they will confuse different versions of the installation document.
Write the installation steps here. The steps should be written in enough detail that an actual user can follow them. You must test the installation process with actual users before shipping the release. Users who have difficulty installing the product can generate expensive calls to technical support.
It can be a good idea to show users how to perform a very simple tasks to prove to themselves that the product is properly installed and working. For example, the Apache webserver will show a default page that simply indicates that the server is up and working.