Anyone can help....
I have installed RH7.3 on my machine. i want to configure my machine to host many sites. http://xxxx.xxx.xxx.xxx works well on the internet. but when i used http://xxx.xxx.xxx.xxx/site1, it aint workin. i just add a dir on /var/www/html.

I don't understand what you want to accomplish. If you want Virtual Hosting, you will need the following

DNS setup:
www.site1.com resolves to xxx.xxx.xxx.xxx
www.site2.com also resolves to xxx.xxx.xxx.xxx
www.site3.com yet again resolves to xxx.xxx.xxx

In /etc/httpd/conf/httpd.conf, under section 3 'Virtual Hosts', you will need to define www.site1.com as /var/www/html/site1, www.site2.com as /var/www/html/site2, etc. When you access the httpd server via the name www.site2.com, you will automatically read the index from /var/www/html/site2. Take a look at the examples in the httpd.conf file for more guidance.

If this isn't the type of set up you are looking for at all, you'll need to refine your question a little more.

i dont have a dns yet,since i didnt register anything.im just learning some new things, a real newbie.

using ip based: http://xxx.xxx.xxx.xxx i can browse the default index.htnl on directory /var/www/html

i made i directory in /var/www/html/jcb for example. then i tried to brwose it http://xxx.xxx.xxx.xxx./jcb it doesnt work but http://xxx.xxx.xxx.xxx/jcb/index.htnml it works

Use Cjb.net, they offer free Subdomains that will point to ur IP domain.cjb.net

i would use an ip based site.and multiple host.just like windows