I have attached the instructions that I used with a friend to set-up Apache for local web hosting on his OSPi. The steps are quite detailed and assume a clean install from a new SD card. As Samer said above this requires a bit of knowledge of Debian and Apache so not for the faint hearted!
Note that hosting the web site “only” gets you a system that is less dependent on the OpenSprinkler cloud services which may be your preference. If you are looking to customise the web app then that is a whole other order of magnitude when it comes to configuring the system for web development. Curious what you are looking to achieve ?
Let me know if the attached helps. Pete