You can add from and size parameters to your search request which will determine the hits that will be returned. To get hits 0-20 set from equal to 0 and size to 20. To get the next page of results, set from to 20, and keep size at 20.
https://www.elastic.co/guide/en/elasticsearch/reference/current/search-request-from-size.html
Be careful of deep pagination and don't let your users go past the first 100 or so pages of search results. If you want to do that, take a look at search_after (https://www.elastic.co/guide/en/elasticsearch/reference/5.5/search-request-search-after.html) or the scroll API (https://www.elastic.co/guide/en/elasticsearch/reference/current/search-request-scroll.html).