They wear this out of humility and respect for Hashem. Yarmulkes come in many shapes, colors and designs. Normally, on Rosh Hashanah, Yom Kippur and Pesach, Jewish men wear white yarmulkes. This represents purity and righteousness. The Torah does not command men to wear kippahs, it is a custom.
Some men only wear a kippah when saying a blessing, when praying, when studying, etc.
Normally Jewish women do not wear kippahs. Thank you for the information on the yarmulke. I have a friend who is a conservative Jew in my class. Even though I am not a Jew, I love reading the Old Testament, and love learning about God, and how he had chosen Abraham to start the Jewish nation. I just saw the movie The Chosen, and now I am reading the book.