Gin-san takes history lessons, and teaches you how to hide your porn mags?
Tsukuyo tries to teach Seita history, the subject he's not great at. However, her training (?) methods end up leaving him scarred, which makes desperate Seita ask Gin-san to take over as his tutor...
Before that, it was just mostly-gorillas 
running around with spears in hand.
فلم يكن هناك سوى غوريلات تجوب المكان برماحها قبل ذلك
Antes de eso solo había 
gorilas corriendo con lanzas.
Antes disso, era só um bando de 
gorilas correndo por aí com lanças.