I am new to these things, and don't know what to do to get my site's http address, who can give me a clear answer?

If you buy a domain then it is your domain name
If you have registered for the free service then you will see it displayed in your account when you log in and select "web hosting".

You might also want to look at my Getting Started help page. Item 2 deals with registering and creating your site address.

I clicked on my http address"crwxs.bravehost.com" but it didn't work. after a few minutes the IE window says "Server Not Found".

May it be a DNS error? If so, I want Bravehost.com to provide me the real IP address of CRWXS.Bravehost.com.
(Maybe DNS server of my city has an error in my site)

the full address of your website would be helpful. And also have you edited it yet? or have you just signed up and not done any changes or anything to it?