Before us are mishnayos in Maseches Berachos. The concept of a berachah recited over a cup is well known, using a cup of wine to recite a berachah over it, and the Mishnah discusses this idea and how essential it is.
Wine brought after the meal:
If wine was brought after they had finished eating, and there is only that single cup there, and the person wants to drink it right away and does not wish to wait until after Birkas HaMazon, we say that he recites the berachah over the wine, drinks it, and afterward recites Birkas HaMazon. This is because according to this opinion Birkas HaMazon does not require a cup, and there is no obligation to recite it over a cup.
According to Beis Shammai, however, Birkas HaMazon is recited over the cup. Therefore one must first recite Birkas HaMazon over the cup and only afterward recite the berachah over the wine, and in this way the wine can be drunk at that same time. In other words, according to their view a cup of wine is required over which Birkas HaMazon will be said.
Answering Amen to another person's berachah:
The final halachah in the Mishnah, which is also the halachah that concludes the entire chapter, deals with answering Amen:
After a Jew who recites a berachah: One may answer Amen even if he did not hear the entire berachah but only its end.
After a Kuti (Samaritan) who recites a berachah: One does not answer Amen until the entire berachah has been heard, because the Kutim are suspected of idolatry. Since it is not known what he said at the opening of the berachah and to whom he directed it, and as long as the words have not been heard we have no certainty about this, one does not answer Amen to his berachah.
With this the halachos of this chapter conclude.