At the moment, there are two ways to create JIRA issues with a CSV import:

• the more limited Creating issues using the CSV importer, not allowing users to create new entities from field values (e.g. new users or versions);
• Importing Data from CSV, only available for JIRA Administrators and providing more flexibility.

At the moment, the first functionality can be accessed from the top bar menu under Issues > Import Issues from CSV, which can be misleading. The documentation for the differentiates between "creating" and "importing" issues from CSV - it would help if the application itself reflected this distinction too.