How to activate SHARE POINT 2013 workflow ??? 

You have configured SharePoint 2013 and Workflow Manager. You have created a new Site Collection. You’re unable to create SharePoint 2013 workflows (but SharePoint 2010 workflows works).

Problem: The site collection was created using the blank template, which doesn’t include all necessary dependency features for creating workflows.

Fix: You need to enable the hidden feature WorkflowServiceStore using PowerShell.

Enable-SPFeature -Identity WorkflowServiceStore –Url yourUrl