Question:

Why do we read four special parshios during the month of Adar?

Discussion: 

The Mishna Berura (685:10) explains that we read these parshios to commemorate different events that took place. The first parsha that we read is Shekalim. The reason for this is that in the times of the Bais Hamikdash there were sacrifices that were brought on behalf of the entire nation. The money for these sacrifices was collected every year during Adar. Therefore, we read the parsha that talk about donating to the Mishkan to commemorate the obligation to give money for these sacrifices.

Parshas Zachor is to fulfill the mitzvah of destroying Amalek. We read it the week before Purim to join the two episodes of Amalek. Since Parshas Zachor is a torah obligation, one should be careful to hear every word that is read. If a person missed a word he should ask a Rav what to do because there is a Machlokes in this matter.

Parshas Para is read to commemorate the first Parah Adoma that was brought in the desert. We read it before the month of Nissan since in the times of the Bais Hamikdash it was important to be spiritually pure so that the Korban Pesach can be brought. Parshas Hachodesh is to sanctify the month of Nissan. 

One does not have to read Shnayim Mikrah on these extra Parshas that we read (Terumas Hadeshen). However, if a person is accustomed to reading the Haftorah before Shabbos then he should read the special Haftorah for these Parshas.

A Woman’s obligation in Hearing the Four Parshas

Women are not obligated to hear any of these special parshios (even Parshas Zachor). If a woman wants to come to shul, she is certainly welcome to. One should not make a special reading for women unless there is also a minyan of men that have not fulfilled their obligation.