Pazar means sunday, how come pazartesi means monday?
Because it's the day after Sunday.
"ertesi" is "following" or "next", so "pazartesi < pazar ertesi" is something like "the one following Sunday".
Similarly with Saturday (cumartesi), which is after Friday (cuma).
it is clear: thank you!
So do we only use "günü" after the day when we speak of it abstractly? Example: On Thursdays we drink beer --> Biz perşembe günü bira içeriz. Or "günü" not in this sentence because it's already part of bugün?