This Shabbat is Shabbat Mevarchim ("the Shabbat that blesses" the new month): a special prayer is recited blessing the Rosh Chodesh ("Head of the Month") of the upcoming month of Av (also called "Menachem Av"), which falls on Wednesday of next week.
Prior to the blessing, we announce the precise time of the molad, the "birth" of the new moon. See molad times.
It is a Chabad custom to recite the entire book of Psalms before morning prayers, and to conduct farbrengens (chassidic gatherings) in the course of the Shabbat.
Links: Shabbat Mevarchim; Tehillim (the Book of Psalms); The Farbrengen
Please click here to view the Yeshivah Shule Tzetel for Shabbos Mevorchim Av, Shabbos Chazak, Parshas Matos Masei.
Details of the Siyumim during the nine days will be sent out next week IY"H.
Moses spoke to the heads of the tribes of the children of Israel, saying: This is the thing which G‑d has commanded (Numbers 30:2)
This verse can also be interpreted as follows: Moses spoke to the children of Israel regarding the heads of the tribes, that they must follow their instructions as one follows the word of G‑d.
(El, "to," can also mean "about"; li, which in this context translates as "of," usually means "to"; thus el rashei hamatot livnei yisrael ("to the heads of the tribes of the children of Israel") can also read, "[And Moses spoke] about the heads of the tribes to the children of Israel, [saying: This is the thing that G‑d has commanded] . . .")
(Alshich)
Moses spoke to the heads of the tribes (30:2)
This was the procedure with all the laws that Moses taught: first he would teach them to Aaron and the heads of the tribes, and then he would instruct the people, as described in Exodus 34:31–32.
Why are the tribal heads particularly mentioned by the laws of vows? To teach us that an expert Torah scholar has the ability to annul vows like a tribunal of three laymen.
(Talmud; Rashi)
https://w2.chabad.org/media/pdf/113145.pdf