To configure connection with selected HubSpot instance, go to Settings (a Cog icon), then Apps and click on the HubSpot CRM Integration link. When you configure the connection for the first time, you need to authenticate by clicking on the Allow access button.
Click on the Allow access button
Click on the Connect button
Click on the Continue button to be redirected to HubSpot page
Select HubSpot instance you want to connect to
At this moment there is no way to restrict integration to selected projects.
In the next step, you can select properties that will be displayed in Jira issues.