If you set the record to private than you and only you will be able to see it (and change).
It does not matter who creates the activity like meeting, task or phone call - you for yourself, someone for you, or you for someone. Make it public (unless you don't want someone to chnage it - in that case use public read-only). It will automatically show on the calendar and the list of activities of all employees assigned.
To view someone's else calendar or tasks use Perspective button: http://www.epesi.org/Top_panel#Perspective
