With the Slack API, you can build integrations with the platform. Such as Messaging individual users or posting to a channel.
The Slack API uses HTTP methods over HTTPS
https://slack.com/api/. The API responds with JSON and an HTTP status code. 2xx for success 4xx for not found and 5xx for service were unavailable.
Authentication with the Slack API uses Bearer Token Authentication. Which you can locate in your Slack account.