What do you need to know about Chinese search engine Sogou?

A few days ago, the news emerged that Chinese search engine Sogou is aiming to raise up to $585 million in a U.S. IPO. The news has caused a stir among those keeping an eye on the Chinese tech space; but for those of us who might not be up on the state of search in China, what do you need to know about Sogou? And what does a Sogou IPO mean for the wider search industry?