Hello Dhayanand,

This article should provide you a good starting point, Nintex Workflow - List to CSV UDA - Vadim Tabakman 

The action List to CSV UDA not found in my list workflow (nintex). as well Web request action in my workflow.

Am using SharePoint 2013 (onprem) with nintex

The article is with reference to Nintex 2013.

You need to create the UDA, with reference to the article.(You can also use the sample files he has attached in the DOWNLOAD section). 

I also see the web-request action in SharePoint 2013 Nintex Workflow Designer Page.

Hi ,can you please explain in detail the flow of the actions in the state machines shown in this UDA creation in the above mentioned article.