This is really easy. You do not need to be connected to the net unless you have the internet option and want to let others use your observatory.
Start ACP.
Click this button to show the ACP Server preferences dialog.
Check the box "Enable Web Server" and "Enable FTP Server". Leave the other settings alone.
Click OK to close the Properties window. Leave ACP running.
On ACP's main window, click the Use Web Browser button.
When the browser starts up, you should see the main ACP web/mobile interface. If you just want to use the ACP browser interface locally (on the ACP computer) that's all there is to do!
If you have the internet option and want to use ACP from a different computer, we need to set up a user account for you. ACP's web and FTP sites require username/password logins unless accessed from the local/ACP computer. This is for your own protection, as you'll see...
If You See a Popup Question or Error
You may see a Windows Firewall (or other personal firewall) message about ACP requesting to be allowed inbound connections on port 80 and 21. You must allow these inbound connections to the ACP web server.
If you see a popup with a very long error message that basically says the web server can't be started, it's virtually certain that you have something else already on your system that is acting as a web server and using port 80. To verify this, reopen server preferences if needed and change the port from 80 to 8765 or some other number above 1024. Click OK and it will probably close OK. Your ACP web server will now be reachable on Port 8765. The Use Web Browser button will work, try it. If this happened, most likely Microsoft Internet Information Server (IIS) which virtually no one outside the corporate world needs. Disable it (using your Windows control panel per your OS version) and try port 80 again. If that's not it use the TCP View utility to find which program has port 80 in use. You may end up deciding to use the non-standard port (8765 in the example here) but your remote users will need to specify the port number in the URL (80 is implicit for the web).