Hi Jujubean! Nice to hear from you again. :)
The doshas give us a way to recognize that people are individual yet have things in common, certain proclivities that add up to a "Dosha" or body type.
The Dosha qualities are also related to illness, so it gives us a shorthand way of speaking - being able to say "That's a Vata disorder" is a great way of saying a lot by saying very little. Knowing that someone has a Vata derangement instantly says that they have too much cold and air and dryness, so to become balanced they need warmth and moisture.
If you are a Pitta-Kapha (most people are a combination of doshas, it's rare to find a single dosha person) person, that means you are prone to Pitta-Kapha imbalances and must balance your Pitta-Kapha tendencies. Pitta stands for "fire" and means Bile from the liver. Kapha means Water or Phlegm, and is all about mucus. So a Pitta-kapha person would be prone to acne, jaundice, asthma, sinus infections, things like that. What usually ahppens is you're more of a Pitta person in the summer, as summer heat aggravates Pitta, and more of a Kapha person in the winter, as the cold aggravates Kapha cold and damp.
If that seems to confusing, then figure out which Dosha rules the symptoms you'd like to eradicate. If you are overweight, that's a Kapha imbalance, so following Kapha guidelines would help you lose weight. If you are easily irritable, sweat a lot, then that's a Pitta imbalance and you should do cooling therapies and diet.
Make sense? :)