Partial answers to some of your questions:

1. What is functional difference between Local and Global configuration ?
You can find information about this in the OSLC Configuration Management primer at https://oslc-op.github.io/oslc-specs/notes/config-primer/config-primer.html. Quoted from that document:

3. In Global configuration , if the one requirement can be available in all streams, then in each stream, will it contain the same unique id or will it contain the different id in different stream? What is conflict strategy, if all users are making changes in same requirement in diff streams ?

Your question is too imprecise to give a meaningful answer. Unless you have performed a component refactor, all versions of a specific requirement will belong to the same component. All versions of thatr equirement will have the same numeric requirement id. Different versions of requirement will have their own versioned artifact URI. If the same version of the same requirement is selected by multiple streams and/or baselines, then the same versioned artifact is referenced in each such local configuration. As described in the OSLC Configuration Management primer (see above), it is common to reference a requirement by its concept URI and a configuration context. If the specified configuration context is a DN local configuration, such as an RM stream, that will resolve to the version of that requirement selected in that specified local configuration. If the specified configuration context is a global configurqation, then as described in the primer, this is first resolved to a local configuration from knowing the component that owns the requirement and the contributiuon tree of the global configuration.

4. Steps to enable global configuration in Doors Ng project.

You first need to visit https://www.ibm.com/docs/en/elm/6.0?topic=applications-considerations-enabling-configuration-management to read and accept the considerations before enabling configuration management (in DN or ETM). That self service page can generate a configuration management license key.

Then:

1. Go to the administration page: https:// fully_qualified_host_name :9443/ application_context /admin.
2. In the left navigation pane, click Advanced Properties.
3. On the application administration page, search (click Ctrl+F) for Local Versioning Component.
4. For the Enter license key to enable configuration management property in that section, in the Current Value field, paste the activation key.

Having done that, in the project area admin page, select thje project area you want to enable. On the left hand panel there is an option for enabling configuration management. Note that once you have enabled a project area for configuration management, you can never undo that operation.