If your server is behind a router, then make sure that port 80 on the router is forwarded to your server. If you want to have FTP access (or SSH, etc) then forward those ports as well.
On any other PC type your IP number in the URL field of a web browser and see what is actually displayed. In case of a router you should see the router's internal web interface with a login page, unless you made the settings as described before.
Having a static IP number for your server on the local network is one thing. To access your server from the Internet you need to know the IP-address of your Internet connection, which should be a fixed IP-number if you truly want to serve webpages to the public.