As you try to compose your answer to this for an assignment, you will need to think of your own in- and out-groups, which will obviously be quite different from those of the eNotes editors answering this question.
There are many factors which go into creating our identities and we are normally members of multiple overlapping groups.
If you are religious, for example, you would regard co-religionists as members of your in-group and people of different religions or atheists as members of an out-group. This type of affiliation affects many elements of your life. For example, you might seeing fasting and donating to charity during Ramadan as normal if your in-group is Islamic, but associate the ostentation of Christmas with the materialism of a religious out-group of Christians.
Another type of identity we have is racial. Even for people who are not consciously racist, often part of building our own identity involves affiliating with people of our own backgrounds, preferring to live in neighborhoods filled with people of certain racial backgrounds. If we see our out-groups as more prestigious and powerful than our in-groups, we might attempt to "pass" for members of the out-group or otherwise assimilate, whereas if the opposite is true we might emphasize our own in-group heritage in our personal lifestyles.
Our gender identities form another set of in- or out-groups. For example, men might feel uncomfortable wearing skirts or makeup as that is associated with the female out-group, but women attempting to succeed in business may want to wear suits, speak with a deliberately lower pitched voice, and otherwise emulate the manners and style of the more powerful out-group of men within patriarchal societies.