Big Ears is an interval driller. It plays a random interval and then allows you to guess which interval was played. (See What is Ear Training.) Each time it plays an interval, it randomly selects a starting pitch. Big Ears has a range of two octaves and chooses pitches chromatically (it does not stick to a diatonic key).
To hear a new interval, just press the big ears in the upper-left corner. This will select a new current interval and play an example of it. You can always hear another example of the current interval by pressing the "Repeat" button just beneath the big ears.
You can guess what the current interval is by pushing one of the interval buttons. These buttons start at "P1" (perfect unison) and extend chromatically all the way to "P11" (perfect eleventh). You can guess as many times as you like; Big Ears will not judge you. After you guess correctly, press the big ears again to hear a new interval.
Each interval button has two other items associated with it, a little ear and a checkbox. You can press the little ear at any time to hear an example of that interval. The checkboxes allow you to turn intervals on or off. An interval which is on is one which may be randomly chosen when you push the big ears. If you are inexperienced with interval drilling, try starting with only a few intervals turned on and then gradually add more. The "All On" and "All Off" buttons in the lower left also control these checkboxes.
Big Ears also allows you to control how it functions with two settings in the lower right. The direction can be set to "ascending", "descending", or "both". When set to a single direction, Big Ears will only play intervals in that direction. It will randomly select a direction each time it plays an interval if "both" is selected. The mode may also be set to "normal" or "help". In "help" mode you can click on any item to learn about its function. The mode must be changed back to "normal" before you can do anything else.
If you still have any questions, or if you have suggestions for future functionality, be sure to send feedback to the author.