I learnt that some people don't open bottles on shabbos because it breaks the perforated seal...what are the details of this halacha? Is it allowed or not? Because I've noticed that some people open bottles while others do not. Also, if the opinion is that we shouldn't open bottles, what if one needs to open the grape juice for kiddush, does the fact that its needed for the mitzvah make it allowed?
Ashkenazic poskim hold that one may not open a bottle with a metal cap for the first time on Shabbos because removing the cap separates the ring from the cap and makes the cap into a useable vessel. One may make a hole using a knife in the cap if there aren’t letters or pictures on it so that makes it unfit for a cap afterwards and then one may open the bottle. 
However, it’s permissible to open a bottle with a plastic bottle cap (because it had the form of a cap before it was attached). Some poskim are strict even with plastic.
Some Ashkenazic poskim and Sephardic poskim hold it’s permissible to open bottles with metal or plastic caps but add that one who is strict to open them before Shabbat will be blessed.
Someone who holds that it’s forbidden to open a bottle on Shabbat is forbidden to ask another Jew who holds that it’s permissible to open a bottle on Shabbat.  However, some say that if one is only strict based on the minhag of his Rabbis or father one may ask someone who holds it’s permissible. 
 Shemirat Shabbat KeHilchata 9:17 (new edition 9:18), Shabbos Kitchen (Rabbi Simcha Bunim Cohen, pg 184-6). [39 Melachos (Rabbi Ribiat, vol 3, pg 841) writes that a less preferable option is to twist off the cap and discard it immediately (and it may be useful to have another cap handy).]
Shemirat Shabbat KeHilchata 9:17 (new edition 9:18), Shabbos Kitchen (Rabbi Simcha Bunim Cohen, pg 184-6). [39 Melachos (Rabbi Ribiat, vol 3, pg 841) writes that a less preferable option is to twist off the cap and discard it immediately (and it may be useful to have another cap handy).] Rav Shlomo Zalman explains that it is forbidden to open a bottle cap for the first time on Shabbos because in the process one is creating a new kli, i.e. a bottle cap that can now be used to cover bottles. While it was attached to the bottle it was not yet a kli, because it could not be screwed on and off of a bottle, which Rav Shlomo Zalman considers the key function of a bottle cap. (Minchas Shlomo 2:32) Also, if one was to break the bottle and slide off the cap as is, without breaking off the ring, it would not be functional as a cap at all. (Minchas Shlomo 1:91:12) However, Rav Shlomo Zalman distinguishes between a metal bottle cap and a plastic bottle cap. The above issues are all in regards to a metal bottle cap. A plastic bottle cap is different, because the ring is thinner, and majority of it is not attached to the cap. Therefore, it is recognizable that the ring is a separate entity from the cap itself and is meant to be removed. Based on this, Rav Shlomo Zalman paskins that it is forbidden to open metal bottle caps and permitted to open plastic bottle caps. Rav Ribiat thinks that the plastic caps that Rav Shlomo Zalman allows, which were from Eretz Yisrael, are different from the plastic caps that we have in America. (39 Melachos Makeh B’Patish footnote 96c). See Meor HaShabbos page 482 who offers a new leniency for plastic caps after researching the production of plastic soda bottles.
Rav Elyashiv (quoted in Orchos Shabbos Perek 12 footnote 31 says that they are all assur to open. Rav Elyashiv holds it’s forbidden to open both metal and plastic caps because of mechateich. Also, Rav Nissim Karelitz (Chut Shani 2:37) says that even by plastic there is an issue of metakein kli.
Rav Ovadia Yosef in Sh"t Yechave Daat 2:42 and Yalkut Yosef (vol 2, pg 517, 675). Rav Ovadia Yosef disagrees with both points of Rav Shlomo Zalman. He thinks that even while the cap is attached to the bottle it is considered a kli since it is covering the bottle (Yechave Daat 2:42). Also, if you would be able to take it off without breaking the ring, even though it wouldn’t fit over a bottle of the same size, it would technically still be usable to cover (albeit not via screwing) a smaller bottle. (Response to Rav Shlomo Zalman quoted in Yalkut Yosef Shabbos Krach Bet 314:18:20) Additionally, the Magid Mishnah (Hil’ Shabbos 12:2) holds that metakein kli is completely permitted if you don’t have intent. Combining his above reasoning with the Magid Mishnah’s leniency, Rav Ovadia paskins that it is permitted to open bottle caps for the first time on Shabbos. Rav Shlomo Zalman disagrees with Rav Ovadia's application of the Magid Mishnah. He explains that even though your main intent is for the drinking, it’s also on your mind to make a cap that would be usable in the future. Nonetheless, Rav Ovadia paskins that it is permitted, and does not differentiate between metal and plastic bottle caps. See also Rabbi Mordechai Willig’s opinion in Am Mordechai (Shabbat, Siman 29, pg 161). Rav Willig agrees that it is permitted. The bottle cap was a kli even before you broke off the ring, and the issur metakein kli is only when you create a kli, not when you merely alter the function of a preexisting kli. (Am Mordechai Siman 29:3)
 The 39 Melachos (Rabbi Ribiat, vol 1, pg 93) writes that it’s forbidden to ask a fellow Jew to open a can or bottle for him on Shabbat if the one requesting holds that one is forbidden to do so. He supports this with Sh”t Igrot Moshe 4:119:5. Many poskim also forbid including Tal Imrati (18:11, pg 190) quoting Chacham Ben Tzion Abba Shaul, Yalkut Yosef (Shabbat, vol 3, pg 217-9) quoting Rav Ovadyah Yosef, Banim Chavivim (Siman 18, pg 91) quoting Rabbi Eliezer Waldenburg (from Meor HaShabbat (vol 1, Peninei HaMeor pg 552)) and Rav Chaim Kanievsky (from Meor HaShabbat (vol 2, pg 77)). Rav Yisrael Belsky in Shulchan HaLevi (vol 1, Birur Halacha 10, pg 339) also rules stringently and gives four reasons. (1) Shelichut LeDvar Avierah. In the Gemara Bava Metsia 10b there is a dispute between Ravina and Rami Bar Chama regarding Shaliach LeDvar Avierah. Ravina holds that there’s only Ein Shaliach LeDvar Avierah when the one being sent is obligated in that prohibition, while Rami Bar Chama says that there’s Ein Shaliach LeDvar Avierah whenever the one being sent has the ability to choose to do it or not. The Rama C”M 182:1 rules like Ravina and so if the one being sent isn’t obligated then there is Shelichut. Rav Belsky concludes that since the one being sent follows a Rabbi who holds it’s permissible to open a bottle he’s considered not obligated in that prohibition and there would be Shelichut. Thus, if he is asked by someone who doesn’t open the bottle there would be a Deoritta violation of Shabbat. (2) Lifnei Iver. Rav Belsky writes that since the opinion of those who hold it is forbidden is that it is forbidden for all Jews it would be forbidden to ask another Jew because of Lifnei Iver. (3) Amirah LeYisrael. He quotes the Radvaz 4:258 who forbids Amirah LeYisrael because it should be no better than Amirah LeNochri. (4) Degrading one’s friend. By asking one’s friend to do something which one holds is forbidden is treating him like a Shabbos goy or a less important Jew. Rav Belsky concludes that it’s forbidden to ask him to open the bottle and it would be just as forbidden to ask him to open it for himself to drink because all the reasons apply except (perhaps) the first one. Though, he agrees that if the one who holds it is permissible opened it for himself it is permissible for others to benefit from the contents of the bottle.
 Rav Shlomo Zalman Auerbach (Meor HaShabbat (Peninei HaMoer 3:8)) rules that if the one requesting holds it’s forbidden based on his ruling, then, it’s forbidden to ask someone who holds it’s permitted to do it for him, however, if the one requesting is only strict because of the minhag of his Rabbis or father, then it’s permitted to ask someone else to do that act.