1. Manual creation
To create publication (issue) dates for your site (magazine/journal/newspaper) make sure your administrator has added the related list to the sites layout.
Navigate to App Launcher - Sites and open a site record .
Click on new to create a new publication date record. Additionally to the actual date of issue which can be selected in the Media Configuration the record allows you to store dates for material deadlines and invoicing which you can use to report and alert staff. The Invoicing Date is also used if you like to use the automated Flexible Payment Plan.
You can also enter general data like the circulation or book size. Have your administrator add custom fields if needed.
Make sure to add an invoice date if you like to use flexible payment plans based on the publication dates.
2. Bulk creation using the Wizard
Please read 4.3.9.2 Publication Date Wizard