The visibility of specific records in the CRM can be limited by the security setting called User can see following records. You can set which records a user will be able to see and which will not show for them. You need to be an administrator to change the security settings.
For a better idea about how the security works, see the diagram below.
Record visibility authorization Settings
A permission to other users' records can only be set by an administrator.
Click the Settings option. 
Select Users Administration button.
Select a user and click on his name.
Select the Change authorization button.
Select the Full throttle, Certain restrictions or Readonly user's role (Administrator can access all records).
Choose whether the user will be able to view the records of all users, only his own records or only the records from selected users.
Save your security settings.
The record visibility setting does not apply to Products. Products are always visible for all users. Only the users with the Certain restrictions or Readonly role do not have the permission to create products.
In the security settings, you can further set: