Answer:
The difference in the category is mainly how rapidly you cycle through moods but both involve depression and mania. Bipolar 2 is a lesser degree of the illness because the mania is only a "hypomania" where you still have a grasp on reality but you have periods of excitedness, more energy. An example of this form is where you get the urge to read about a certain topic, buy 5 books on the topic and immediately lose interest and find something else to do, on and on.
With Bipolar 1, this is where you cycle very frequently from mania, (previously called, manic-depressive disorder) to severe lows, depression. A person in this category can reason highs to the point where they become delusional and feel higher than life and lack good judgment (like thinking you can run off to another country in one day then getting there and feeling absolutely incapable).