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.
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 are also groups of users but are organized in a hierarchy. Users in ...