We will controlling our WP as usually.
you need to login first on yourdomain.com/wp-admin then manage your wordpress from usual wordpress layout, not from cpanel.
Try it for free webhosting first like 000webhost.
Well, I'm using 000webhost but it is not supporting fantastico installer temporarily, so I'm not able to install wordpress scripts.

Suppose if I create a blog in wordpress.org website, I will have website name like this "http://www.mysitename.com/wordpress.org, right?
How to add my custom domain inside the wordpress.org website? Are there any option to add custom domain?