Can anyone let me know how to create Workflow for sending an email.!
It would be as easy as adding a new workflow step within your workflow model. You can use the AEM out of the box "Day CQ Mail Service" to send out emails; make sure you Configure AEM to use a Mail Server.
Watch this 16 minutes youtube video to walk through step by step on how to send out an email within starting a workflow process - https://www.youtube.com/watch?v=F8fYQuZ8cwI
Tutorial - https://helpx.adobe.com/experience-manager/using/creating-custom-aem-workflow-steps.html
Click here for a tutorial for Mail Server Set up in AEM using GMail - https://adobeexplorers.com/2019/06/09/mail-server-set-up-in-aem-using-gmail/