Hola Rachela, hay una pagina de informes ya hechos por gente que puedes aprovechar
Te recomiendo que tengas los conceptos basicos de SQL al menos un poco claros, sino esto se hará un poco cuesta arriba.
Aun asi, te adjunto dos informes para sacar los informes de logins y logouts(dos distintos)
LOGINS
SELECT concat(u.firstname ,' ',u.lastname, ' ', u.username) AS Username
,COUNT(*) AS logins
,(SELECT COUNT(*) FROM prefix_log WHERE userid = l.userid GROUP BY userid) AS Activity
FROM prefix_log AS l JOIN prefix_user AS u ON l.userid = u.id
WHERE `action` LIKE '%login%' GROUP BY userid
ORDER BY Activity DESC
LOGOUTS
SELECT concat(u.firstname ,' ',u.lastname, ' ', u.username) AS Username
,COUNT(*) AS logins
,(SELECT COUNT(*) FROM prefix_log WHERE userid = l.userid GROUP BY userid) AS Activity
FROM prefix_log AS l JOIN prefix_user AS u ON l.userid = u.id
WHERE `action` LIKE '%logout%' GROUP BY userid
ORDER BY Activity DESC
Un saludo