Elasticsearch's search_as_you_type field datatype simplifies the creation of autocomplete functionality for search engines by breaking down text into n-grams, which are partial sequences of words or letters. This approach allows for rapid matching of partial text inputs as users type their queries. The process involves indexing data with the search_as_you_type datatype, generating subfields that facilitate quick retrieval of search results. The tutorial demonstrates the implementation of this functionality using the MovieLens dataset, showcasing how to index data, perform searches, and utilize the multi-match query along with the bool_prefix type for effective autocomplete suggestions. This technique enhances user experience by providing relevant search predictions with each keystroke, and the tutorial further explores advanced features like edge n-gram token filters and the use of the jq command-line tool for handling JSON data in Elasticsearch.