How to configure multiple domains pointing to different directories on a server

I'm assuming you want to host multiple sites on a single IP address and that you're using apache. If so, then essentially, the following lines of code in my httpd.conf do the job for me:

NameVirtualHost a.b.c.d:80

<VirtualHost site1.company.com:80>
    DocumentRoot /path/to/site1/documentroot
    ServerName site1.company.com
    CustomLog /usr/local/apache/logs/site1.company.com.access combined
</VirtualHost>

<VirtualHost site2.company.com:80>
    DocumentRoot /path/to/site2/documentroot
    ServerName www.brossi.net
    CustomLog /usr/local/apache/logs/site2.company.com.access combined
</VirtualHost>

Where a.b.c.d is your server's IP address. Repeat VirtualHost declarations as you need them. The CustomLog declaration isn't vital, but it helps me to keep my sites' logs separately from one another.

You can find more documentation on apache at http://httpd.apache.org/docs/; click on the version of your apache server, then enter (eg) NameVirtualHost in the search box (though the doco for that can also be found directly at http://httpd.apache.org/docs/current/mod/core.html#namevirtualhost - it's not a feature that changes much between versions).