While you are in CareerPlug's Onboarding system, navigate to your Settings page (Account > Settings). In the Checklist section, click the New Checklist button.

Choose whether you want to create an employee or a manager checklist:
Choose checklist type

When you create a new checklist, you'll most likely want to check the box next to "Part of the Onboarding Process" to have the option to have the checklist assigned to new hires.
When you create the checklist, you have the option to add forms you've created or non-form steps. When you add a form, you can add a deadline by completing the Complete By Days field. Add as many steps as you need by clicking the Add New Step button. 
Checklist Step

Click Create Checklist at the bottom of the page when you're done, and you're ready to assign the checklist to an employee or new hire.