A Biblical or Rabbinical obligation? There are opinions who say that there is a Biblical obligation to hear Parshas Parah. [Many Poskim however argue and rule there is no Biblical obligation to hear Parshas Para.]
Making sure to be with a Minyan for Parshas Parah: Being that the reading of Parah is a Biblical obligation [according to some Poskim], it is required that one arrange to be in an area that has a Minyan for that Shabbos.
If no Minyan is available: If a Minyan is not present on Shabbos for the reading of Parshas Parah, the portion is nevertheless to be read [without a blessing] with its proper tune.
When: When [the second day of] Rosh Chodesh Adar falls on Shabbos, Parshas Parah is read on the fourth Shabbos in Adar which is the 22nd of Adar. When [the second day of] Rosh Chodesh Adar falls on Monday or Wednesday Parshas Parah is read on the third Shabbos of Adar. When Rosh Chodesh Adar falls on Friday, Parshas Parah is read on the fourth Shabbos in Adar which is the 23rd of Adar.
Which portion is read? The Torah portion for Parshas Parah is read from Parshas Chukas, from the words “Vayidabeir Hashem El Moshe Leimor Zos Chukas Hatorah…” until the words “Titmah Ad Haerev”. The Haftorah of Parah is read from Yichezkel, from the words “Vayehi Dvar Hashem Eilay Leimor..” until the words “Ani Hashem Dibarti Vaasisi”.
What is the law if one did not read until verse 22, [“Titmah Ad Haerev”]? If the Baal Korei stopped before verse 11 [“Lageir Hagar Bisocham”], then if the blessing recited after the Torah reading was not yet said, they are to continue the reading until verse 22. This applies even if the Sefer Torah was already rolled up. If however, an after blessing over the Torah was already said, then even if the Torah scroll is still open, they must read the entire portion again from the beginning, and recite a new blessing before and after for the Aliyah.
How many Torah scrolls are removed and what is the order of reading: Two scrolls are removed from the ark. [The Torah scroll is to be rolled to its proper section before Davening in order to prevent delay for the congregation.] From the first scroll the entire weekly Torah portion is read until [and including] Shevii. The second scroll is then placed on the Bima which is followed by half Kaddish. Hagba is then performed to the first scroll. One may not open the second scroll until the first scroll is rolled up and placed in its Meil. [The Mi Shebeirach for the ill is recited after Hagba.] For Maftir the portion of Parah is read from the second scroll. [On Shabbos Mevarchim the Chazan for Musaf takes the scroll of Maftir to hold.]
Can one make up the hearing by Parshas Chukas:
One who could not be with a Minyan by Parshas Parah can seemingly make up his obligation with the eventual reading of Parshas Chukas.
Are women obligated to hear Parshas Parah?
If the Baal Korei skipped a verse in the reading of Parshas Para is one Yotzei?
If he skipped any of the verses between verses 1-10 he is Yotzei. If however he skipped a verse between 11-22, then if the verse discusses the main matter that the Sages required one to read in this Parsha, one is not Yotzei. If, however, the verse does not discuss the topic of the Parsha, one is Yotzei. However, there are Poskim that rule one is always Yotzei irrelevant of which verse was skipped.
What is the law if a congregation read Parshas Parah a week early?
Some Poskim rule one is to read it again the next Shabbos. Others rule he is Yotzei and it thus does not need to be repeated the next week. Practically one is to repeat the reading.
 Michaber 146:2; 685:7; Admur 282:16 only mentions Parshas Zachor
 Tosafus Haketzaros Brachos chapter 2; Aruch Hashulchan 685:7; Arugas Habosem O.C. 205
 The source: Some rule this is learned from the words “Lechukas Olam” written by Parah Aduma. This teaches us that one is to read the portion annually. [Aruch Hashulchan ibid] Others rule that it is learned from the words Lo Tishkach which is said regarding the Eigel. [Arugas Habosem ibid]; See however M”A 685 who questions as to what is the source for this
 Peri Chadash 146; Shlah; Bach; Rashal 182; Tosafus Shantz brought in Kaf Hachaim 685:28; M”B 685:15; See M”A 685 who questions as to what is the source for this
 Michaber 685:7
 Rama 685:7
 Reason why it is read before Hachodesh: The reason why we read Parshas Parah before Hachodesh is because it discusses the purification of the Jewish people and is thus given precedence. [Rashi Megillah 29a; Kaf Hachaim 685:19]
 Levush brought in Kaf Hachaim 685:26
 Chapter 19 verse 1
 Chapter 19 verse 22. As the entire Parsha until this verse discusses the matter of purification. [Kol Bo 20; Levush; M”B 685:10; Kaf Hachaim 685:20]
 Chapter 36 verse 16
 Chapter 36 verse 36
 The first ten verses only hint to the Mitzvah of Parah Aduma and hence do not suffice for one to fulfill his obligation. [M”A 136:11]
 The Rama 136:5 rules that if they already closed and rolled up the Torah Scroll, then the entire reading must be repeated from the beginning, with a Bracha before and after. The majority of Achronim however explain that this “rolling” is not to be taken literally and rather if an after blessing was not yet made, even if the Torah was already rolled up, one may still return to the reading. [Elya Raba; Shaareiy Efraim 7:4; Mishneh Berurah 136:17] The P”M 136 M”Z 4 explains that this rolling up refers to returning the Torah to the Aron.
 Elya Raba; Shaareiy Efraim 7:4; Mishneh Berurah 136:17
The Reason: One must repeat the reading with a Bracha because the first reading was unlike the institution of the Sages and was thus invalid. [M”B ibid]
Other Opinions: The Taz 136:4 rules that so long as the Torah has not yet been rolled up [and put away in the Aron-P”M 136 M”Z 4] they may continue with the reading, even if an after Bracha has already been said.
 Mishneh Berurah 685:9, 12
 Pashut as this is the entire reason for why we are to take out two Sifrei Toras
 Michaber 147:8; Kol Bo; Elya Raba 147:9; Kaf Hachaim 147:42
 See Shaar Efraim 10:41; Piskeiy Teshuvah 150:4
 See regarding Zachor: M”A 685:1 and so rules Beir Heiytiv 685:2; P”M 685 M”Z 12; Shaareiy Efraim 8:85; Minchas Elazar 2:1; Kaf Hachaim 685:28; Aruch Hashulchan 685:5; Hisorerus Teshuvah 1:5; M”B 685:8; Mahril Diskin 2 Kuntrus Acharon 5:111
 Piskeiy Teshuvos 685:6Nitei Gavriel 22:4
 Setimas Kol Haposkim, who although discuss whether women are obligated in hearing Parshas Zachar make no mention of Parshas Parah.
The reason: Several reasons can be suggested for why women are exempt: 1) The making of the red heifer ash is a community obligation, and is not upon women. 2) It is a time-dependent command which applies before Passover. 3) It is read in order to atone for the sin of the golden calf, which women did not participate in and do not need atonement for.
 See Otzer Minhagei Chabad 240 that makes an implication from Sichas Parah 1976 that even women are obligated; Shut Chayeh Asher 84 who writes that in his family they would make sure the women listen to Parshas Parah.
The reason: As women are obligated in the Pesach sacrifice, and hence they too should need to hear this reading. [Mikraeiy Kodesh]
 M”B 136:18; Elya Raba 136:10
 M”B 136:18
 M”A 136:11
 See Kaf Hachaim 685:23
 As ruled earlier regarding one who read Parshas Shekalim a week early.