LEFT JOIN
takes all the details from the table you define on the left side of the join and match records from the right table.
If there's no match, all columns of the right table have NULL values.
If there's a match, all matching records from the right table are returned. If your relationship is 1-to-many (as in your case), it means that there may be more than one record returned from the right table for each record in the left table.