a part of an adjective or pronoun = 新的， 你们的 or a part of possessive case / descriptive construction 昨天 买的 书 在 哪儿？

的，是表示所属的一个词 的（de）Is a word that belongs to 例如：你的，我的，或他/她/它/的 For example：your（yours），my（mine），or his/her/its 你的书（your book) 我的书（my book） 或他的书（or his book） 那是我的包（that is my bag.(or：that bag is mine) 你明白了吗？ do you understand?

Usually has four pronunciations(de、dí、dì、dī), I give you some examples. If you want to know more you can ask me in private. 1.的 de （1）用在定语后，表示词与词或短语之间的修饰关系[-ic,-ve…]。如：红色的气球(hóng sè de qiǘ)。小小的进步(xiǎo xiǎo de jìn bǜ)。 (1) after the attributive, said the modified relation between word and the word or phrase[-ic,-ve…].. . Such as: red balloon. A little progress. （2）用在定语后，表示定语和中心词之间的领属关系[of,'s]。如：中国的水稻。（zhōng guó de shuǐ dào）农民生活的提高。(Nóng mín shóng huó de tí gāo ) (2)after using attributive, said "relations between the attributive and the center word [of, 's]. Such as: Chinese rice. The improvement of farmers' life. （3）〈代〉pron.附着在词或短语之后，构成“的”字结构，代替所指的人或物。如：卖菜的。(mài cài de )吃的。(Chī de) (3)pron. Attached to the word or phrase, “of” the word structure, instead of referring to people or things. Such as: the man who selling vegetables. Food. ……and so on 2．的 dí,〈副〉adverbs （1）确实；实在[really；indeed]————的（dí） （2）又如：的对；的据（真凭实据）；的觉（果然；的确）；的是（的确是） （2）Such as: the right; According to a (relatively); (indeed as expected; indeed); Are （3）必定；一定[certainly]。如：的决（处决；处斩）；的的（特意） (3) must be; A certainly. Such as: definitely (executed; chop); The (specially) 　 3. 的dì (1).目标、靶心。2.明显、明确。3.确实、落实。4.关于目标。用为所有格oftarget） (1). The goals, the bull ‘s-eye. 2. Clear and clear. 3. Indeed, the implementation of the. 4. About the target. Use for the possessive oftarget) (2) 箭靶的中心 (2)centre of target for archery (3)鲜明的样子。 (3) [bright] 4.的dī 的士 Commonly known as the taxi. i hope this answer can help you .:)