please tell me why should one learn the ORACLE  RDBMS PRODUCT  because i dont know any thing about
the oracle and now i can't decide which RDBMS product i should learn so please tell me some unique features
about the oracle.and other things is that  there are so many RDBMS product in a market so i want to know that
why oracle is so popular and if possible give me some url from where i can get lot of resources for oracle.

Oracle popular? Depends on who you ask. An international company I worked for wouldn't touch oracle (way too instable for them), it maintained IBM & MS SQL.

Of course, what's popular depends on who you ask, where you are, and how much money the person gets for selling the product.

Offhand, I think SQL is the cheapest, IBM's the second, Oracle the most expensive. I've seen independant reports that conflict as the which is the better.

For Unique features, go to Oracle's website (and IBM's, and Microsoft's) for compariason charts.