Log in as an admin, go to "user maintenance" and add them into the groups.
https://confluence.atlassian.com/display/JIRA/Managing+Users#ManagingUsers-Assigningausertoagroup
Option 1 : Goto Administration > User Management > Groups > Select the group and Add
Option 2: Goto Administration > User Management > Select the user > Add group
It looks like you're new here. Sign in or register to get started.