One of the workhorse parts of speech in English and in most European languages is the relative pronoun. These include that, when, which, who/whom/whose, where and a few other less frequently used ones. Usually they modify or specify nouns: “the restaurant where we ate last night/that we ate at last night,” “my neighbor who is always playing drums late at night,” etc.
Chinese has no relative pronouns. In fact it has very few pronouns at all, except for a few that function both as subject and object pronouns when you insist on mapping English grammar terms on to Chinese sentences —他 (he/him), 她 (she/her), 它 (it). (Note that adding 們 (men) after any of these characters makes it a plural pronoun. Can you tell I love grammar yet?)
So how do you duplicate the function a relative pronoun performs in English,
for example “I really like the cake that Michael brought”? Just as an English relative pronoun often modifies some noun, the Chinese way of expressing that idea is similar. The writer of the Chinese sentence uses the possessive marker 的(de) to create some (perhaps a long) phrase that “modifies” the noun by “possessing” it. A simple example of the use of 的 is “his car” (他的車). Here 他的(tā de) is quite similar to the possessive adjective “his.” But the same rule is used to create longer phrases. For example, “I really like the cake that Michael brought” is 我真的喜歡邁克帶來的(那個)蛋糕 (Wǒ zhēnde xǐhuān Màikè dài lái de (nèige) dàngāo).
Relative pronouns being so important in European languages yet unknown in Chinese, the sooner you can get the hang of this the more rapidly you will be able to create more complex Chinese sentences.