What is RankBrain?
An AI algorithm developed by Google to sort search results and search queries is known as Rankbrain. It is considered to be the third most important ranking signal.

Before RankBarin all the algorithms were hand-coded by Google engineers.

For example:
When Google Engineers develop an algorithm it was tested manually. If the results were good and produced good results they would make the algorithm permanent.

But, the RankBrain algorithm will sort the search queries and results and implements the algorithm on its own. If the desired result is achieved the new algorithm stays or else it reverts to the old algorithm on its own.

How Does RankBrain Work?
In the older days before RankBrain was developed by Google, it would match the search queries word by word on a page to get the user the result they are looking for.

But, RankBrain thinks like a human mind. When you type a search query it tries to figure out the concept of the phrase and matches them with keywords Google has already seen to give a better result.

In Other words, It is mainly used to interpret the searches that people submit to find pages or links that might not have exact words.

So, you might think about, how does it will affect my rankings.

When a user or visitor searches using a search query RankBrain will show them a set of results based on their query.
If a webpage or an article get most clicks and dwell time the RankBrain automatically will push the page up higher in search engine rankings.
Therefore people spending more time on your website will send a good positive signal to RankBrain.

If users don't engage with your article or webpage it will send a bad signal to RankBrain. So next time when the same search query comes up your article will be replaced with some other related article.

How to Optimize for RankBrain?
1) Try focusing more on Medium tail keywords.
yes, you heard that right;
When you optimize a content using a medium tail keyword RankBrain automatically ranks you for that exact keyword and some other similar keywords.
Brain Dean in his article on Google RankBrain shared some statistics where is medium tail keyword not only ranked for the exact match but ranked for other 1.8k keywords along with it.

2) Make sure to add title and Meta description with emotion in it.

3) Include keywords in your title and meta description.

4) Keep your intro short and get to the point quickly, like what the user can expect in this article. This will increase the dwell time and decrease the bounce rate.
This will send a good positive signal to RankBrain to push your website up on the rankings. Because at the end of the day Google wants to provide good quality content for their users.