Hi Srinu, this page wil answer all your questions: https://help.salesforce.com/apex/HTViewHelpDoc?id=custom_field_types.htm. In few words, lookup fields simply links one entity to the other: if you delete the object that is linked, the one that has the lookup fields simply sees that value blanked. In the Master detail relationshpip, if the father is deleted, the children are deleted as well. There are other behaviors that you find in the guide.
this page wil answer all your questions: https://help.salesforce.com/apex/HTViewHelpDoc?id=custom_field_types.htm.
In few words, lookup fields simply links one entity to the other: if you delete the object that is linked, the one that has the lookup fields simply sees that value blanked.
In the Master detail relationshpip, if the father is deleted, the children are deleted as well.
There are other behaviors that you find in the guide.
May the Force.com be with you!
Enrico