"Execute Selected" it is a little improvement allowing you to create multiple issues with fewer clicks.
You can perform bulk operations on a project level (on Scheduled Issues you have access to) or from administration section.
Here is an example: Log in as a user with Jira administrator rank and head to "Add-ons" (1), then go to "Manage Scheduled Issues" (2).
Next, select scheduled issues (3), of which you would like to create standard Jira issue of particular type and use "Execute Selected" (4) button:
"Execute Selected" button displays how many issues have been ticked.