In your hppd.conf file you you should have:
This means that the Apache web server is available on port 80 which is the default port for http://
You also need to include a line like:
The IP addrress is the IP address of the PC running the Apache web server.
If your IP address is dynamic (assigned by a DHCP server) then you have a problem because the address you give out to your friends will change from time to time.
You may be able to get the LAN administrator to assign you a fixed IP address.
(Look at the TCP/IP properties for your network card - if it says obtain an IP address automatically then you have a dynamic IP address that will change sometimes on boot up).
You can't use the typical www.mydomain.com because
(a) you don't have a domain name and
(b) there is likely no DNS server to provide the translation from the name to the variable IP address.
If you are on a larger LAN it is possible that there is a DNS server (such as BIND) - ask the LAN administrator.
If your IP address is fixed, then anyone on the LAN should be able to access your Apache web server.
Just ask them to enter http://192.168.0.50 or whatever your IP address is, in a browser.
You should also be able to access the server on your own PC with the same line instead of 'localhost'.
IP addresses over a LAN are 'private' and are not accessible over the internet.
You should also consider your security settings in Apache.
Without security settings anyone can access your web server pages, including folders that you may be using for page development etc. etc.
Apache comes with password management and there is lots of info. on this from the Apache project.
In httpd.conf you should also have:
Deny from all
to prevent .htaccess and .htpasswd files from being viewed by Web clients.
.htaccess should be in the root of your Apache docs folder (default is htdocs).
the .htaccess file is plain text and includes the address of the password file, which should not be stored in the htdocs folder.
As to firewalls, you will have to look at the firewall you are using e.g., AVG or Norton and follow instructions for ports, and see if port 80 is open. Look for something like network protocols in the firewall section and then http protocol incoming. This varies a lot from product to product.