When identifying and singing Triads by ear, it helps to remember the intervals that make up a specific triad.
The following chart is a review of the intervals that make up each triad.
For a more complete review of Triads go to Understanding Triads.
For help on singing 3rds see How to Hear Thirds.
To identify a triad by ear, listen carefully to the bottom and top interval to see what type of 3rds make up the triad and in what order from top to bottom.
To sing a triad, you will need to be able to sing the correct type of 3rd for the bottom and top intervals. Here is where all of your practice with intervals will become very important, especially the interval of a 3rd. To do these exercises you will need to have a firm grasp on hearing and singing major and minor 3rds.