Complex sentence: Rabbi Gedalya Sternstein, also American born, learned in Ner Israel Yeshiva of Baltimore under Rabbi Y. Ruderman, and thereafter in Mercaz Hatorah in Montreal, where he was "mashgiach".
Split into simpler sentences: Rabbi Gedalya Sternstein was born in America and learned in Ner Israel Yeshiva of Baltimore under Rabbi Y. Ruderman. Thereafter he learnt in Mercaz Hatorah in Montreal, where he was "mashgiach".