Responsible is the owner and/or team member who work with an object. 

On accounts, contacts and opportunities you can add several users as responsible. On leads (unqualified deals), tasks, Call lists, campaigns and Appointments you can only have one responsible.

Work together

Add the colleagues you want to work with on the account, contact or opportunity. They will then 

- See this object in the personal list

- Can interact with the object

- Be notified in realtime on their smartphone when another user add, update or remove something form the object.

Split the deal

(This is for opportunities only)

In Edit Opportunity, click on a team members name to set how to spilt the sales value between the members.