doshas are not easy to fully grasp. one aspect of them is easy. but they are also subtle. they can be thought of in physical terms but also you can think of them in psychological and energetic senses.
physical is easiest. gas, bile, and phlegm. remember that dosha can be thought of from one view as a blemish.
but you have to understand the gurvadi gunas, the 20 qualities, that arise from the play of the five elements. see the first chapter of the sutrasthana of the Astanga Hrdaya for the clearest view.
you can simplify this to the upakarmas (3 pairs)
1. hot-cold
2. heavy-light
3. moist-dry
and remember the doshas that makes up our constitution (prakṛti) and the elements (tattvas which are referred to as mahābhūtas)
vāta = vāyu + ākāśa or wind/gas + space = dry, cold and light body qualities
pitta = tejas + jala or fire + water = hot, light and moist body qualities
kapha = jala +pṛthvī or water + earth = heavy, cold and moist body qualities
so to treat the imbalances you usually use the opposite qualities
so ayurveda gives a very simple means to think about the imbalances and treat them... but it's not always that simple... you can always go deeper and see that the approach isn't always opposite (e.g., Tadarthakari Chikitsa where you use similar properties). and the doshas have sub-divisions that let you be even sharper in your treatment
