Or think of a library and you are searching for a particular book. If you did not have an index you would have to search every shelf. If you have an index then you would go to the section/shelf/row/book... Basically, indexes shorten the path to the record(s) that you are trying to retrieve.
thnx rnealejr for the information.. So is the indexing basically on dba side, means while creating the table itself we need to declare the index.And in query we wil access particular row using the index number.I am using Oracle Db.So any online site where can I get the indexing sqls to get the overview..