I dont want to use de standard ringtone as my ringtone. I want to put my favorite song as my ringtone. put a mp3 song as my ringtone
As an option, you can install Winamp, play your mp3 you want to set as ringtone and click Menu -> Set as ringtone.
You have to install an app if you want to use ringtones besides those that come with the phone. I use GO SMS Pro. It's free and comes with a lot of features. You can even assign a different message tone per contact. You can download it free from Google Play.