Two or more Jews who share a courtyard or hall, each of them living in his own apartment, are forbidden on Shabbos to carry from their apartment into the courtyard or hall, or from the courtyard or hall into their apartment. It is therefore considered a mitzvah for them to make an eiruvei chatzeiros.
The procedure is as follows. Erev Shabbos, one of the tenants takes a whole loaf of bread and confers a share of it to all tenants of the courtyard by handing it to another tenant and saying in whatever language he understands: “Take this loaf of bread and acquire it on behalf of all the Jews who live in this courtyard.” This person then takes the loaf and raises it one tefach. The one who is making the eiruv takes it from him and recites the following berachah:
בָּרוּךְ אַתָּה יְהֹוָה Blessed are You, Adonoy
אֱלֹהֵֽינוּ מֶֽלֶךְ הָעוֹלָם our God, King of the Universe,
אֲשֶׁר קִדְּ֒שָֽׁנוּ בְּמִצְוֹתָיו Who sanctified us with His commandments
וְצִוָּֽנוּ and commanded us
עַל מִצְוַת עֵירוּב: concerning the mitzvah of eiruv.
בַּהֲדֵין עֵירוּבָא By means of this eiruv
יְהֵא שָׁרָא לָנָא it will be permissible for us
לְאַפּוּקֵי וּלְעַיוּלֵי. to take out and to bring in
מִבָּתִּים לֶחָצֵר. from the houses into the courtyard
וּמֵחָצֵר לְבָתִּים. and from the courtyard into the houses
וּמִבַּיִת לְבַיִת. and from one house into another,
לָֽנוּ וּלְכָל יִשְׂרָאֵל. for all the Jews
הַדָּרִים בֶּחָצֵר הַזֶּה: who live in the houses of the courtyard.