ElasticSearch integration replaces build-in MySQL FULLTEXT or regular search with ElasticSearch. This integration requires ElasticSearch server.
It can be useful for the sites with a lot of data to leverage search on another server and free MySQL from this task. Also ElasticSearch can return more relevant search results.
If you are adding this module to the site with existing content, then you need to index all existing data, it can be done from ElasticSearch module configuration page in Studio.
This module works with site search by keyword and don't work with custom search, but we'll add custom search support in the future.