You will not be tested on this in your exam, Saraa.
Nevertheless, I will explain.
The Greeks had no scientific knowledge - their religion was RATIONAL (ie common sense thinking-things-through)
They liked to connect eveything together - as in this diagram:

If you look at it, you can see how it connects the four humours to the four elements, and to their nature (hot or cold, wet or dry) ... and also to a person's nature (melancholic, for example, comes from the Latin word for 'black', and we still talk of people being in a 'dark' mood).
This diagram does not show the seasons of the year, but I bet you could put them on the document at the correct corners fairly easily.
Illnesses, the Greeks believed, occurred when the humours got out of balance.
An excess of blood might lead to a florid skin, or a fever (we know today that high blood pressure DOES cause illness) and would cause the person to be over-passionate or over-optimistic ('sanguine' comes from the latin word for blood), and so it would be treated by bleeding or leeches.
An excess of yellow bile would cause vomiting (puke
is yellow) and would lead the patients to be angry (the word for anger 'choleric' comes from the Greek word for bile, and we still say that someone is bilious), so it would be treated with an emetic to make them vomit.
An excess of black bile would be characterised by stomach upset and diarrhoea - so the doctor would purge him.
And of course, an excess of phlegm would cause a cold or flu, and the doctor would prescribe an expectorant (which we still do, of course).
Just before I finish, look again at the chart, and at the characteristics of the elements/humours.
Can you see that Black bile is 'cold and dry', phlegm is 'cold and wet' etc.
the Greeks decided that was HOW you got got an excess of a humour - what caused it. If you had gone out in winter in the rain and got too cold and wet, you would get an excess of phlegm, and catch a cold.
So what is the cure - to keep the patient hot and dry! (We still say much the same for a cold today!)
And if you;d gone out in the sun too long in summer, and got too hot and dry, and got an excess of yellow bile, and had caught sunstroke - surely the best treatment is to keep the patient wet and cool (which indeed it is).
This explains why Hippocratic medicine involved the 'use of opposites'.