there are a number of existing threads that might help. If you look to the right under "Releated Community content" you will find some or you can also search using the Search bar at the top of the page.
Here is one that has a number of good references - zoho-to-jira-intergration
here is an article on CSV import - creating-issues-using-the-csv-importer
here is a post that discusses importing attachments - Does-importing-issues-from-another-system-with-attachment
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