[RajatPawar]

You use a variable to check if a player is viewing a menu or not. Then you use another variable to store the current menu choice which will change under OnPlayerKeyStateChange when a player uses the KEY_UP or KEY_DOWN buttons. When the player key state changes, you highlight that particular row using TextdrawSetColor or you can even offset the row to give a shadow effect using the YSI plugin continued by kurta999. Make sure you check for all cases like (selection row number isn't greater than the number of rows itself..)