Translation:Shulchan Aruch/Orach Chaim/56
56: LAW OF THE CONGREGATION'S RESPONDING TO THE KADDISH. Contains 5 seifim.
1 One should have concentration when answering to the kaddish. Gloss: And one should not interrupt between "Y'hei Sh'meih Rabba" and "be blessed" [Hagahot Asheri in the name of Or Zarua wrote that according to the first explanation, one should not interrupt between "Sh'meih" and "Rabba", and according to the explanation of Ri, one should not interrupt between "Rabbah" and "be blessed"]. And one should answer it loudly and strive to run to hear Kaddish. Gloss: And one should stand when answering Kaddish and any matter in which there is holiness. And one who comes to synagogue and hears the congregation answering Kaddish answers along with them even though he did not hear the prayer-leader saying "Yitgadal etc." [Hagahot Chadashim on the Mordechai of Brakhot]. And the prayer-leader also needs to say "Y'hei Sh'meih Rabbah...". And when he begins "Yitgadal...", one should say "And now, let the power be magnified etc., Remember Your mercy etc.".
2 When the chazzan says: "yitbarakh", everyone answers "amen", and so too when he says "b'rikh hu", and so too when he says "v'imru amen". And we do not practice to say "amen" after "yitbarakh" and not after "b'rikh hu". And one should not interrupt between "b'rikh hu" and "l'eila mikol birkhata etc.".
3 Those who respond up until "l'olmai olmaya" only – they err, for it is forbidden to interrupt between "olmaya" and "yitbarakh".
4 When the chazzan says "Yitgadal", he bows, and similarly at "y'hei Sh'meih Rabba", and similarly at "yitbarakh", and similarly at "b'rikh hu", and similarly at "amen".
5 After one finished the kaddish, one steps 3 steps and then says "Oseh shalom etc.".