When sharing tasks or entire plans with teams and individuals, access rights can be set :
A reader can see the properties of a task, but not edit them. She cannot see its permissions.
An editor can change, add, and delete tasks. She can read permissions, but can't edit them.
|Manager permission||A manager has free access and can edit everything. She can edit permissions and place new ones.|
Of course, roles can be changed later on and permissions can be removed at any time.
Get to know your responsibilities
The owner is a particular person managing access rights. When changing the ownership the old owner gets read access to this object.
A person being the responsible for a task automatically gets Editor rights to that object. But note that only persons having access to the project can be set as responsible.