I have created a custom list named “K2 Workflow Tutorials” in which K2 workflow will be created to create a subsite. Please refer to my previous article to create a K2 workflow in SharePoint 2013 Online.
Go to K2 designer, drag and drop Create Subsite step from the Sites Workflow Steps in the ribbon interface.
Specify properties for the subsite and then click OK button.
Deploy the workflow. Create a new list item in “K2 Workflow Tutorials” list with THE title field value as “TEST SUBSITE” and description field value as “Test subsite created using K2 workflow”. After few minutes the workflow will be completed and a new subsite will be created with the title as “TEST SUBSITE”.