how create a group of users

[KasiaCC]

I want to create a group of developers, that can see only a one board for their project. How i can make it?

[Nic Brough -Adaptavist-]

You need to remove the right for all users to automatically see everything first - look at how "JIRA users" group is used in projects to grant the right to see things.  Once you've unpicked that (replace "can log in" rights with another group, or remove jira-users from all places it's defaulting the right to see issues), you'll be able to create a group that can only see one project.