What are groups in SFDC and what is their use?

Groups are sets of users. They can contain individual users, other groups, the users in a particular role or territory, or the users in a particular role or territory plus all of the users below that role or territory in the hierarchy.

There are two types of groups:

• Public groups: Only administrators can create public groups. They can be used by everyone in the organization.
• Personal groups: Each user can create groups for their personal use.

You can use groups in the following ways:

• To set up default sharing access via a sharing rule
• To share your records with other users
• To specify that you want to synchronize contacts owned by others users
• To add multiple users to a Salesforce CRM Content library
• To assign users to specific actions in Salesforce Knowledge