What is Shnayim Mikra v'Echad Targum?
R. Huna b. R. Yehuda said in the name of R. Ami that a person should always complete the weekly Torah portion with the congregation, reading the text (mikra) twice and the translation (Targum) once. This applies even to “Ataros and Divon.” (See Numbers 32:34 – according to Rashi, these are place names that have no translation.) One who learns Shnayim Mikra v'Echad Targum will have his days and years extended (Talmud Brachos 8a-b).The Aruch HaShulchan (O.C. 285:2) considers learning Shnayim Mikra v'Echad Targum to be a rabbinical obligation.

What counts towards Shnayim Mikra v'Echad Targum?
By “Targum,” the Talmud refers to the Targum Onkelos, the Aramaic translation of (and commentary on) the Torah. Numerous authorities, including the Rosh (Brachos 1:8) and the Tur (O.C. 285), say that the commentary of Rashi is also acceptable. Some – including the Shulchan Aruch (O.C. 285:2) – maintain that it would be appropriate for one to study both Rashi and the Targum. (This statement does not seem to express a preference for one over the other.)

Tosfos (Brachos 8a, “Shnayim”) acknowledge the opinion that any translation of the Torah into one’s own language is acceptable, but they do not conclude agreeing with this opinion, since Targum Onkelos is a unique combination of translation and commentary. The Mishna Brurah (285:5) concludes that if one cannot understand the commentary of Rashi, he may use a translation that conforms with the traditional interpretations of the text as per the Talmud, Rashi, etc. (The Mishna Brurah gives the example of the book Tzena u’Renah in Yiddish.) This is what the Orthodox Union’s Shnayim Mikra does: it provides a daily lecture on every aliyah of each weekly portion that explains the text in accordance with the teachings of the classic commentaries on the Torah.

When does one start learning the weekly portion?
The Talmud does not define the times for reviewing the weekly portion. Tosfos (Brachos 8b, “Yashlim”) writes that the earliest time to begin studying a portion is after Mincha (the afternoon service) on Shabbos, when we begin reading that portion. (See also Shulchan Aruch O.C. 285:3 with the commentary of Mishna Brurah 285:7; for another position, see below.*)

By when should one finish it?
Tosfos (ibid.) say that one should optimally complete learning Shnayim Mikra v'Echad Targum before eating the first Shabbos meal, though it is also possible after eating, so long as one finishes before Shabbos is over. The Shulchan Aruch (285:4) cites two surprising opinions. One position permits a person to finish learning Shnayim Mikra v'Echad Targum until the following Wednesday. (This is based on the fact that one may recite havdalah, the ceremony ending Shabbos, as late as Wednesday if one forgot or was unable to do so in the proper time on Saturday night.) The second permits one to finish as late as Simchas Torah, when we complete the entire Torah cycle. So, while it is certainly proper and appropriate to complete a weekly portion before Shabbos is over (Mishna Berura 285:12), one may rely on the opinion that permits it until Simchas Torah (Aruch HaShulchan 285:10).

*(According to the opinion that one may complete until Simchas Torah, the obligation to study Shnayim Mikra v'Echad Targum is an annual, rather than a weekly one. Accordingly, some contemporary authorities permit one to “get a head start on” upcoming Torah portions.)

What about the haftara?
There is no obligation to study the weekly haftara Shnayim Mikra v'Echad Targum, but it is preferable to do so. (See Rema 285:7.) The Orthodox Union’s Shnayim Mikra provides supplemental material (in text form) elucidating the weekly haftara; participants may also wish to study the appropriate selection using the OU’s Nach Yomi.

What about holiday portions?
The readings of holidays and other special occasions do not have to be learned Shnayim Mikra v'Echad Targum because the weekly portions from which they are taken are read during the year anyway. (See Mishna Brurah 285:18.) The exception, of course, is Simchas Torah, on which we read V’Zos HaBracha, the final portion of the Torah.