Hi Sir/Madam,
I have already bought a registered domain from other site. How can I use web hosting service for it from x10hosting?
Your first step would be to login at your registrar to configure the domain to use our name servers. They are ns1.x10hosting.com and ns2.x10hosting.com
Then you need to answer this question, do you want it to point to the same site as
http://alanhung.x10hosting.com?
If yes: you should add it as a parked domain.
If no: You should add it as an addon domain. In this case it will act as a completely different site, and all files will be located in a separate sub folder of public_html.
Both these options are done through cPanel, you'll find them in the "Domains" section. For both options you just fill in the required information (for parked the only thing required is the domain name, without www).
Note that changes to dns, such as explained above can take 48 hours to fully be updated, though in most cases it is rather fast.