Client user acces

Client user acces

Hi there,
I  ve created a client user for a project and I want give him only access to some documents or task, but it seems he has access to another documents which I dont want to show him. How is the structure of client user acces? by task, by documents,etc... ? I know there is 2 categories, internal or external, but I use the internal feature and the client can see documents in my other task, how can configure this  issue?

Thanks