You don't. Jira's permissions are permissive, not restrictive.
To do this, you need to remove whatever it is that is giving your user access to the projects you don't want them to see, and then grant them the permission to see that one project. Take a look at how the "JIRA users" group is being used - you'll need to unpick that if you've still got the defaults.
Atlassian Summit is an excellent opportunity for in-person support, training, and networking.Learn more
Connect with like-minded Atlassian users at free events near you!Find a group
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no AUG chapters near you at the moment.Start an AUG