TRIGGER syntax:

CREATE TRIGGER name
[BEFORE | AFTER] [INSERT | UPDATE | DELETE]
ON tablename
FOR EACH ROW statement

BEFORE or AFTER on trigger is action time to indicate when trigger activities statement activated.
INSERT or UPDATE or DELETE is event indicates the kind of statement that activates the trigger.

How to drop the TRIGGER ?, use DROP TRIGGER order following with table name and trigger name. And the syntax is like this:

DROP TRIGGER tablename.triggername;

Here they are the example case use trigger:
For inserting prosess:

CREATE trigger tr_input before INSERT ON user
FOR each
ROW
BEGIN
INSERT INTO master_user( id, name, pass )
VALUES (
NEW.id, NEW.name, NEW.pass
);
END$$

For updating process:

CREATE trigger tr_update before UPDATE ON user
FOR each
ROW
BEGIN
UPDATE master_user set id=new.id, name=new.name, pass=new.pass
where id=old.id;
END$$

For deleting process:

CREATE trigger tr_delete before DELETE ON user
FOR each
ROW
BEGIN
DELETE from master_user where id=old.id;
END$$

The SELECT privilege for the subject table if references to table colums occur via OLD.col_name or NEW.col_name
The UPDATE privilege for the subject table columns are targets of SET NEW.col_name=value assignment.

Note: in this case I use two table user and master_user. And the scenario is when I input some data or something else into user which automatically updated into master_user.