Translation:Ağustos yılın sekizinci ayı.
Yil is year, what is yilin? And what does the "in" suffix in general?
And it takes the possessive since it's "of the X".
in Turkish both the possessor and the possed thing gets a suffix. So -in here is the genitive suffix. These are already explained in tips¬es ;) https://www.duolingo.com/skill/tr/Possessives