User Groups

Record-level sharing operates on groups of users, not individual users. Force.com provides
two mechanisms for grouping users relevant to sharing: Public Groups and Roles.

Public Groups

At its simplest level, a public group is a named list of users included in the group.This list
can also contain other public groups.To define a public group, click Setup. In the Administration
Setup area, click Manage Users -->Public Groups.
A best practice for public groups is to keep the membership list as short as possible.
This improves performance and simplifies maintenance. Build larger groups up from
smaller subgroups rather than working with individual users.

Roles

Roles are also groups of users but are organized in a hierarchy. Users in roles can inherit
the privileges of the roles below them in the hierarchy.This includes record ownership.
A user belongs to one role at a time, and all applications in your Force.com organization
use a single role hierarchy.

To define roles, click Setup. In the Administration Setup area, click Manage Users -->
Roles.The first time you use this feature, Force.com asks you to select a sample set of
roles to get started.