I'm new to sharepoint 2013 workflows. How do you create a workflow that will automatically email users every six months?
You can use Pause for duration action in designer workflows.
Or you can create site workflow and schedule it to start after every 6 months.
Another option could be to set up a PowerShell script in the task manager on one of the servers in the farm. This will give you the flexibility you will need as the requirements changes like "for this kind of content the reminders should be every 3 months"