You can find examples in our documentation on https://developers.calamari.io. Here is an example of CURL with the authorization headers.
curl --request POST --user calamari:API_KEY --url https://CALAMARI_DOMAIN.calamari.io/api/leave/request/v1/find --header 'content-type: application/json' --data '{"from": "2018-01-01","to": "2018-12-31","employee": "[email protected]"}'