Friday night: There is no prohibition of talking during Kabbalas Shabbos. But if this will disturb others who are praying, then it is forbidden. Also, the speech must be appropriate for the shul. Between Barchu and Shemone Esray, the same laws apply on Friday night as during the weekday Ma’ariv. After Shemone Esray, during Vayichulu and Magen Avos (until after Kaddish before Aleinu) it is forbidden to talk.