Using a SELECT command to retrieve data on MySQL
The SELECT starts off by saying "give (select) me these columns" from this table that connects or joins to these other two tables in this way and where this rule is true.

So you figure out what columns names you need for the results.

Then you figure out how to connect all of the pieces together (foreign key here connects to some primary key there).

Then you add a where clause to filter out unwanted data.

Select p.first_name, p.middle_name, p.last_name, 
  c.subject_name, c.level_of_entry
From classes c 
Inner Join entries e on e.class_id = c.class_id
Inner Join pupils p on p.puil_id = e.pupil_id
Where c.exam_board = 'WJEC'