Hello, someone know where I can find the functions documentation with details?
For example, the core_enrol_get_enrolled_users functions requiere a parameter courseid, but how do you know that? In this documentation there isn't such information: https://docs.moodle.org/dev/Web_service_API_functions
Is there another source of more detailed documentation? with parameters and REST verbs, for example?
Built into the Moodle admin screens, where you configure the web services, you can access documentation for all the web services functions, which is generated from the information in the code, so you can be sure it is up-to-date for your version of Moodle.
To add to Tim's answer - you need to enable web service documentation generation - the details are in the Moodle docs: