To accept or decline a friend request, sign in to Orkut and look for your friend requests at the top of your homepage. Click yes or no to accept or decline it. Don't worry, this person won't receive any message if you refuse the invitation.
Also, if you don't want someone to send you a friend request or a message, add that user to your ignore list. To ignore someone, visit the person's profile and click actions on the top of the page, and choose ignore from the drop-down list.