Synagogue refers to:
The place where physically, practicants of Jewish religion get together to render worship, study, the term Synagogue comes from the latin Sinagoga, and from the Greek synagogue, that means to come together. In the Hebrew is written as Bet haKenéset בית הכנסת
Sabbath is considered in Jewish religion :
The day of rest, for Jewish practicants, is important to rest after the 6 days that are believed to be the time God took when creating everything around us, according to the Genesis, the first book inspired by Moses. It is mandatory to Jewish belief to rest on Saturday.
Kosher then is:
the etiquette especially referring to meals, where the Jewish prescriptions are referred, according to ancient rituals and that is safe to be eaten by believers of Jewish tradition.