Query regarding the dyndns?
 

I have an application in my company PC running on Fedora Linux.
Can dyndns be used to access from outside world?

No, chances are your company pc will be using a private address (rfc 1918) and there will be a firewall present

kdp,

How can I provide access to my intranet PC to outside friend?

Does your friend work for your company?? "My friend" and "My company PC" surely don't fit together. If he needs access then you get it by having your companies network admins or helpdesk line provide it. It's not YOUR PC, it's theirs, and you surely don't have the right to do this.

That was just an assumption. Just want to be familiar with the concept.
How can I let client to login to my machine?

You have not given enough detail about how your PC is connected to the Internet, or any other network. Without those details, no one can give you useful advice. It seems probable that you will have to gain the cooperation of a network administrator to accomplish your objective. The only thing that can be said for certain is that dyndns has little or nothing to do with the issue.
--- rod.