Set the master category
Staying within the admin interface, navigate to Settings > General and you’ll find a new section called Magazine Settings. Here you can set the master category and the current (that is latest) issue.
Posts in the master category act as an issue. When you publish a post in this category it not only updates the current issue value with post’s issue but also publishes all other posts in the same issue that have a status of pending.
The master category is also used by the [backissues] shortcode.
You can also set the current issue. This should be a drop-down box consisting of the Issues that you created in Step 2. When you implement issue-based publishing on an existing site, you’ll likely want to manually set the current issue.