Initials and finals
Unlike European languages, clusters of letters – initials (simplified Chinese: 声母; traditional Chinese: 聲母; pinyin: shēngmǔ) and finals (simplified Chinese: 韵母; traditional Chinese: 韻母; pinyin: yùnmǔ) – and not consonant and vowel letters, form the fundamental elements in pinyin (and most other phonetic systems used to describe the Han language). Every Mandarin syllable can be spelled with exactly one initial followed by one final, except for the special syllable er or when a trailing -r is considered part of a syllable (see below). The latter case, though a common practice in some sub-dialects, is rarely used in official publications. One exception is the city Harbin(simplified Chinese: 哈尔滨; traditional Chinese: 哈爾濱), whose name comes from the Manchu language.
Even though most initials contain a consonant, finals are not always simple vowels, especially in compound finals (simplified Chinese:复韵母; traditional Chinese: 複韻母; pinyin: fuyunmu), i.e., when a "medial" is placed in front of the final. For example, the medials [i]and [u] are pronounced with such tight openings at the beginning of a final that some native Chinese speakers (especially when singing) pronounce yī (Chinese: 衣; , clothes, officially pronounced /í/) as /jí/ and wéi (simplified Chinese: 围; traditional Chinese: 圍, to enclose, officially pronounced /uěi/) as /wěi/ or /wuěi/. Often these medials are treated as separate from the finals rather than as part of them; this convention is followed in the chart of finals below.
Here is a awesome link you can hear and practice the pronunciation!