an administrator, you can add users or Jira groups to project roles. Please, follow the steps below:
Jira Cloud: go to Projects > choose your project > Project Settings > People > click on Add people (button on the right upper side, see also the Atlassian documentation for more information) Jira Data Center: go to Projects > choose your project > Project Settings > Users and Roles > click on Add users to a role (button on the right upper side, see also Managing project role membership) | 
