how do you instal the game after instaling origin

First off, let me start by saying welcome to EA’s “Answer HQ”.
Answer HQ isn't just an ordinary message board or support center. It's a new approach to our community experience and a fun way of helping other players or to get answers (from players & experts)and get back in the game!

1) You must loogin to Origin software with your Email or Origin ID;

2) Go to MY GAMES within Origin software & press right mouse button on NFS Rivals's Icon & choose Download.

If you can't see NFS Rivals under MY GAMES, then you must redeem the game's key!

http://help.ea.com/en/article/redeem-your-serial-code-in-origin/