:( So anyone can tell em how can i do publish only one portal of DNN website not other ???

You really don't need the Content Staging capability to do this. There are a variety of ways you can handle it and the best approach really depends on a number of factors primarily revolving around what types of changes you're making to the child portal. 

In most cases, the best/easiest approach is to go ahead and deploy the whole DNN instance to your production server. You can then point the appropriate URLs to your Main Portal to make it live. If you are primarily making content changes to the child portal, I would go ahead and setup a temporary url (i.e. dev.mysite.com) for the child portal and just make the changes you need to make directly on your production server. Since you are just making content changes, there shouldn't be any risk to your main portal.

If your making code changes to your child portal, I would continue working on those on your development server until the code changes are complete and then roll those changes out once complete. You should definitely be thinking about how you will handle migrating your code changes once they are are complete. We generally use Beyond Compare or WinMerge to migrate code changes and we put all database changes into scripts that we can run on deployment. In some cases, we package up everything as DNN modules and use that as our deployment scheme. But the best approach really depends on the changes you are making.

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David O'Leary
Efficion Consulting