This feature is available Team edition only.
Lifecycle users are called members. These are the people who make up Agile teams, ScrumMasters who coach and remove impediments, Product Owners who manage and prioritize backlogs and Executives who guide and check on progress.
In Lifecycle Team Edition, a system administrator can create and manage up to 10 member accounts. Once set up, members can access the project and perform all related tasks.
Having trouble figuring out what edition of Lifecycle you are using? See How do I know what edition I'm on? to learn more.