What is a summary of the the poem "Breaking Out" by Marge Piercy?

This powerful narrative poem expresses the speaker's first rebellious act. She introduces the subject as if in reply to the question: "What was your first political act?" In reply she states what she perceived and how she responded to the circumstances in which she found herself.
The first stanza, in the present continuous tense, effectively conveys the immediate nature of her recollection. She is reliving her memories as if they are happening at the time of recall. This suggests their power and the impact they have made on the speaker. The fact that she refers to two doors that are usually open suggests that they offer her an unrestricted escape route: a journey she is unable to undertake at the time since she is subjected to her parents' will.
Doors are commonly seen as symbols of either freedom or oppression, depending on whether they are open or shut. These doors are personified and compared to "gossips" almost as if they are leaning towards each other to whisper scandal and rumor, either about the household or the speaker. The fact that they form a closet enhances the element of secrecy and mystery. This is further emphasized by the use of the word "corner," which suggests something inappropriate and secretive.
It soon becomes evident why the speaker expresses suspicion of the doors. It is as if they, along with other objects around the house, are symbols of domestic oppression. The speaker refers to a number of instruments of domesticity. It becomes clear, though, that these objects are utilized to perform acts of overzealous domesticity. The mangle, for example, is used to iron items which ordinarily would not need such treatment. This powerfully conveys the idea of how much her mother takes to the commission of her housewifely duties.
The vacuum cleaner is also personified and seems to be clearly tired and exasperated by the repetitious and unending nature of domestic work. The speaker uses it as a symbol of herself—she has also grown tired of performing these duties. She expresses how much she hates the fact that her mother so willingly submits to the completion of her tasks and affirms that she has decided never to subject herself to such punishment once she finds independence (leaves home).
The allusion to Sisyphus, a character in Greek mythology who was sentenced to forever roll a huge boulder up a hill only to see it roll down again, reminds her of her mother, who, she believes, is suffering the same fate.
In the second part of the poem, from stanza 5 onward, the speaker relates the punishment she has to endure at the hands of both her parents. They use a yardstick to mete out punishment whenever they believe that she is disobedient. The stick, which her mother uses in her occupation as a dressmaker, becomes a reviled instrument of torture to the speaker. She cries out loudly when beaten, but the beatings continue.
The speaker states that her mother's beatings are much fiercer than those of her father, but that his punishment is prolonged and tougher. After such punishment she explores the welts from the blows in a mirror and sees in them blue and red mountains, which become symbols of her desire to be free of the harsh and restricted life she is subjected to. Her veins and arteries become tokens of the routes she will take once she has escaped her life of drudgery and abuse.
The speaker states that she has reached a turning point at age eleven—on the cusp of adolescence. She takes the despised object of torture and breaks it into little pieces—wood that can be used to start a fire. This act also becomes a metaphor for her rebellion. She is surprised that the object, which has been used to oppress and suppress her will, can break so easily. Its power has been diminished to nothing. It is at this point that the speaker, emotionally and intellectually, emancipates herself from the oppression that she has been enduring as a child. She has advanced into the first stages of adulthood and freedom. She has, symbolically, started a fire which will burn, fiercely and forever, within her.
This is strongly affirmed in the final stanza: 

This is not a tale of innocence lost but powergained: I would not be Sisyphus, there were things that I should learn to break.

The speaker states that she has empowered herself when she commits this act. She proclaims that she will not be a slave to drudgery and hard labor and that she has to learn how to break from convention. Her freedom lies in the fact that she has started a journey in which she will shatter society's expectations and demands that she should be submissive, subservient, and obedient just because she is a woman.