$servername = 'localhost';
        $username = 'username';
        $password = 'password';
        $dbname = 'moodle';

        $u_moodle = 'theusernameyouwant';
        $hp_moodle = password_hash('thepasswordyouwant', PASSWORD_DEFAULT); ///IMPORTANT!
        $name = 'first name';
        $lname = 'last name';
        $email = 'e@m.ail'; ///This have to be verified by you as we're inserting it directly
        $course = '123'; //Id that you put in moodle admin, not the real id

        $conn = new mysqli($servername, $username, $password, $dbname);

        $sql = "INSERT INTO 'mdl_user' (auth, confirmed, mnethostid, username, password, firstname, lastname, email)
    VALUES ('manual', 1, 1, '$u_moodle', '$hp_moodle', '$name', '$lname', '$email')";
// auth = 'manual', confirmed = 1, mnethostid = 1 Always. the others are your variables

        if ($conn->query($sql) === TRUE) {
            echo "OKTC";
        } else {
            ////Manage your errors
        }

        $sql = "SELECT * FROM $m_user WHERE email='$email'";
        $result = $conn2->query($sql);
        if($row = $result->fetch_assoc()) {
            $id = $row['id']; //Id of newly created user. we're using that for to register him on the course
        }

////You have to use this if your idnumber for the course is the one you put into moodle (thats not the real id)
        $sql = "SELECT id FROM 'mdl_course' WHERE idnumber=$course";
        $result = $conn->query($sql);
        if(!$result){
            ///Not existing course, manage your error
        }
        if($row = $result->fetch_assoc()) {
            $idcourse = $row["id"];
        }

///I need now the "enrol" id, so I do this:
        $sql = "SELECT id FROM 'mdl_enrol' WHERE courseid=$idcourse AND enrol='manual'";
        $result = $conn->query($sql);
        if(!$result){
            ///Not enrol associated (this shouldn't happen and means you have an error in your moodle database)
        }
        if($row = $result->fetch_assoc()) {
            $idenrol = $row["id"];
        }

///Lastly I need the context
        $sql = "SELECT id FROM 'mdl_context' WHERE contextlevel=50 AND instanceid=$idcourse"; ///contextlevel = 50 means course in moodle
        $result = $conn->query($sql);
        if(!$result){
            ///Again, weird error, shouldnt happen to you
        }
        if($row = $result->fetch_assoc()) {
            $idcontext = $row["id"];
        }

///We were just getting variables from moodle. Here is were the enrolment begins:

        $time = time();
        $ntime = $time + 60*60*24*$duration; //How long will it last enroled $duration = days, this can be 0 for unlimited.
        $sql = "INSERT INTO 'mdl_user_enrolments' (status, enrolid, userid, timestart, timeend, timecreated, timemodified)
VALUES (0, $idenrol, $id, '$time', '$ntime', '$time', '$time')";
        if ($conn->query($sql) === TRUE) {
        } else {
            ///Manage your sql error
        }

        $sql = "INSERT INTO 'mdl_role_assignments' (roleid, contextid, userid, timemodified)
VALUES (5, $idcontext, '$id', '$time')"; //Roleid = 5, means student.
        if ($conn->query($sql) === TRUE) {
        } else {
            //manage your errors
        }