Is Orchestration concept is achievable in Appian? Is so, how can we achieve?...

What do you mean by Orchestration Concept? In general, BPM is doing process and task orchestration. Is there something particular you're looking for?

Yes. I mean to know on how appian supports it? It will be better if you can describe the same

I would suggest you start here and look into the links that would give you some good idea.
www.appian.com/.../appian-business-process-tools.jsp