The api base url will be your site's domain, site api path and the module being accessed.

Example base url:
http://www.sitedomain.com/site_api/[module name]/[specific module endpoint]

Please refer to the individual module documentation for specific module endpoints.

Also please note that if your website has a SSL Certificate, it is recommended that you access the API using https ( ie. https://www.sitedomain.com/site_api/[module name]/[specific module endpoint] )