You can install the Jira WebPart solution in your Sharepoint directly from the Sharepoint Store.
Click on the Settings cog wheel icon on the top right of your Sharepoint
Click on “Add an App”
Search for “SharePoint Connector for Jira” in the search bar
Click on the item in the store
Click on “Add to Apps Site”
Confirm the App Availability options and click on “Add”
Wait for the app to be installed. You will see a message on the top left corner.
You can start using the WebPart! See how here.
You can read more about on how to add an app to a site here.