Berachos, Chapter 3, Mishnah 3. This mishnah addresses the question of which mitzvos women and minors are obligated in, and which mitzvos they are exempt from.
The wording of the mishnah: "Nashim va'avadim uketanim peturim mikri'as Shema umin hatefillin, vechayavin bitefillah uvimezuzah uvevirkas hamazon" - women, slaves and minors are exempt from the recitation of Shema and from tefillin, and they are obligated in prayer, in mezuzah and in Birkas HaMazon.
The groups listed in the mishnah:
"Nashim va'avadim" - women and slaves. Slaves here means a Canaanite slave, who is obligated only in those mitzvos in which a woman is obligated.
"Uketanim" - and minors, children who have not yet reached the age of bar mitzvah.
The exemption from Shema and from tefillin:
The recitation of Shema and tefillin are both mitzvos she'hazman gramma, mitzvos that depend on a particular time, and therefore women are not obligated in either of them. In the case of minors there are additional reasons for the exemption:
From the recitation of Shema: even a minor who has reached the age of education is not obligated in Shema, because minors are not regularly together with their fathers at the time when Shema is recited.
From tefillin: minors cannot be relied upon to maintain a clean body, that is, they cannot necessarily hold back from passing wind, and therefore they are not obligated in the mitzvah of tefillin until they reach the age close to bar mitzvah.
"Vechayavin bitefillah" - and they are obligated in prayer:
All those listed in the mishnah are obligated in prayer, since when it comes to prayer, everyone needs Hashem's mercy. Regarding women, the Rambam writes that the mitzvah of prayer is a positive mitzvah that is not bound by time: it is a daily mitzvah that fundamentally has no fixed time, and for that reason women are obligated in it.
Mezuzah and Birkas HaMazon:
Besides prayer, women are also obligated in mezuzah, since this too is a positive mitzvah that is not bound by time, and likewise in Birkas HaMazon after eating.
It is worth noting that the Gemara is uncertain whether women are obligated in Birkas HaMazon from the Torah or only by rabbinic enactment. On the face of it this is not a time-bound mitzvah, and therefore women should certainly be obligated in it. The Gemara's doubt, however, rests on the fact that part of the mitzvah is based on the words "for the good land that He has given you," and the land was not originally apportioned to women, even though in certain circumstances, such as the case of the daughters of Tzelofchad, where there were no male heirs, women did receive a portion in the land. Since the land was not given to women from the outset, the Gemara is uncertain whether their obligation is from the Torah or rabbinic. In any event, by rabbinic law women and minors are certainly obligated to recite Birkas HaMazon.
In summary: in this mishnah we learned that women, slaves and minors are exempt from the recitation of Shema and from tefillin, since these are time-bound mitzvos, and in the case of minors two further reasons were added: that they are not with their fathers at the time of Shema, and that they cannot maintain a clean body. They are, however, obligated in prayer, since everyone needs Hashem's mercy, and according to the Rambam prayer is not a mitzvah that depends on time; and likewise in mezuzah and in Birkas HaMazon, which are also mitzvos not bound by time, except that regarding Birkas HaMazon the Gemara is uncertain whether the obligation of women is from the Torah or rabbinic.