could add the right-footed and left-footed players that have an overall rating greater than 80 together?
SELECT preferred_foot , count ( * )  FROM Player_Attributes WHERE overall_rating > 80 GROUP BY preferred_foot
add together refers to SUM or COUNT based on context; right-footed and left-footed players refers to preferred_foot; overall rating greater than 80 refers to overall_rating > 80;