There are a number of different approaches to this depending on whether you want to do a one-time import or retain a link between the content in MS Project and JIRA.
If all you want is to import once and stop updating MS Project then the easiest approach is to create a CSV file as explained here. https://confluence.atlassian.com/jira/importing-data-from-csv-185729516.html
However, if you want to retain a link then you need to consider a plugin. Here are some options.
There are other options that you may also want to research depending upon your exact requirements.
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