I have created a custom list named “K2 Workflow Tutorials” in which K2 workflow will be created to create folder in document library. Please refer to my previous article to create a K2 workflow in SharePoint 2013 Online.
Go to K2 designer, drag and drop Create Folder step from the Documents workflow steps in the ribbon interface.
Select a site collection, enter the folder name and then click Next button.
Specify the document library in which you want to create the folder and then click Finish button.
Deploy the workflow. Create a new list item in “K2 Workflow Tutorials” list with title field value as “TEST”. After few minutes the workflow will be completed and the new folder named “TEST” will be created in the document library “K2 Workflow Documents”.