回乡偶书

回乡偶书 -贺知章

少小离家老大回，
乡音无改鬓毛衰。
儿童相见不相识，
笑问客从何处来？

Coming Home

I left home young and not till old did I come back,

My accent was unchanged, but my hair was no longer black.

The children I met don't know me,

They smiled and asked “where do you come from?”

无风不起浪

无风不起浪 wúfēngbùqǐlàng

It simply means nothing happens without a reason, similar as the meaning of “No smoke without fire” in English.

人山人海

人山人海 (rén shān rén hǎi) 
This is commonly used to describe a lot of people, or a very crowded situation.