What's the use of BeginEdit/EndEdit when used with a datarow

Question

1.What's the use of BeginEdit/EndEdit when used with a datarow 2. When a datarow variable needs to be created, e.g. DataRow dr=new DataRow(); It gives the error:"No overload for method 'DataRow' takes '0' arguments" Why such error. If I simply use Datarow dr, then no error. 3. Will the find method work on table having primary key? I mean if there is no primary key, then how to find the record? 4. When I write DataRow dr; int aa=Int32.Parse(textBox1.Text); dr=ds.Tables[0].Rows.Find(aa); It gives run time error that table has no primary key, though it is present. 5. What's the syntax to retrieve a particular value of a field of a row using datarow.