In learning to distinguish major from minor, a good place to start is with major and minor thirds. Here are the basic definitions of major and minor thirds:
The Major Third
The interval sounds smooth and free of tension. That is to say, it is a consonant interval. It conveys a feeling of stability. The distance between the two notes of a major third comprises two whole-steps.
The Minor Third
Like the major third, this interval sounds smooth and free of tension -- consonant -- though it perhaps sounds a little less out-going, a little more somber, than the major third. The distance between the two notes of a minor third comprises one whole-step and one half-step.
Hearing Major and Minor Thirds
That's really all there is (conceptually) to major and minor thirds. The important part is learning to distinguish them; for some of you that will mean developing a very new kind of skill. Listen repeatedly to the examples of major and minor thirds below. The tones are presented both successively and simultaneously; you should be familiar with both forms. When you feel that you can tell the difference between the examples below, go on to the training environment for major and minor thirds.