Disposing objects

Question

Hi,

Iam working on an application where objects are more often have to be dynamically created!!!

How can i dispose the following objects completely from memory?

a form object
class object
dataset object
strings etc 

By assigning null only its reference is lost and not the object?

Can anyone tell me the correct way of disposing these objects?

Also is it proper to use Dispose method for all objects?

Hoping for a better answer!!!

Thanks