This is the 8636th most frequent Chinese word.
z
The letter "z" is not a word in Chinese, as Chinese characters are used instead of the Roman alphabet. If you are referring to pinyin (Romanized Mandarin), "z" represents a sound similar to the "ds" in "kids."
The word "是" (is) establishes an identity, linking "他" (he) to "我的朋友" (my friend).
他是我的朋友。
He is my friend.
The word "的" is a particle indicating possession, linking "今天" (today) to "天气" (weather).
今天的天气很好。
Today's weather is great.
The word "喜欢" (like) expresses personal preference.