This serves to annul our vows (that are able to be annulled) so we can enter Rosh Hashana without the sin of unfulfilled vows, or the sins of not maintaining the performance of good deeds and customs that we have done 3 times or more, which would then in effect give them the status of something that was accepted as a vow. (This is why it is so important to always say "Bli Neder" when promising to do something or when doing something new which you aren’t sure if you are able to always do).
 
2) I heard the following  fascinating  insight from Rav Yissocher Frand shlita in the name of Rav Yosef Dov Solveitzik Ztz"l, to explain why we place such importance on annulling vows on Erev Rosh Hashana, and then do it again at the onset of Yom Kippur (with Kol Nidrei), when seemingly there are more important things to focus on at this most elevated time.
 
The correct definition of the word Teshuva (which is what we are all working so hard to attain at this time) is "Return" and not "Repentance" as is commonly used.
 
Teshuva means "returning to Hashem" and "Turning back the clock" to before we sinned, and erasing the sin from our slate. This idea of "annulling" our sins and making them disappear is similar to what takes place when we annul our vows!
 
When one annuls his vows, the Halacha is that he has to be able to say that he never meant to make the vow in the first place, and that would he have known then what he knows now, he never would have done it.
 
Thus, we show Hashem that we are sorry for all the vows we didn’t fulfill, and they were all made "by mistake" and therefore we annul them.
 
This explains the connection between Nedarim and Teshuva! They work exactly the same way!

We tell Hashem that we want to "return" to Him, and  that all our sins were done "by mistake" and we didn’t mean to do them, and therefore Hashem goes ahead and annuls them.
 
This also explains the sequence of Kol Nidrei at the onset of Yom Kippur:
a) We start with  Kol Nidrei (We tell Hashem that we regret all the vows-and all our sins)
b) We then say The Pasuk "V’Nislach L’Kol Adas Bnei Yisroel...Ki Kol Ha’Am Bishgaga" (which alludes to the fact that all our vows- and our sins- now attain the status of having been done "Bishgaga- by mistake")
c) We recite the Bracha of "SheHechiyanu V’Kimanu V’HiGiyanu..." (Hashem annuls our vows- and our sins- thus we say the Blessing which is recited when one experiences a situation of extreme joy, and is there a greater joy than Hashem accepting us back, and allowing us to return to Him?)
 
[I know that wasn’t technically Halacha, but I just had to share that with you, so you would have a deeper and clearer understanding of why the Hataras Nedarim process is so integral to the Yemei Hadin! ]
 
 
Halachos for Shabbos Kodesh

1) If one doesn’t understand the meaning of the words of Hataras Nedarim (as it is printed in the Siddur or Machzor in Hebrew) it isn’t valid. Therefore it is better to say it in English or any other  language that you understand, or to read it and its translation beforehand so you will know what you are saying when you say it. (Chayei Adam and Kitzur Shulchan Aruch)
 
2) Women do not have the custom to say Hataras Nedarim (One of the reasons for this is that doing so in front of 3 men is not Tzanua). Rather, a married woman should have her husband say to the "Bais Din" that his wife appointed him a Shliach (messenger) to annul her vows, and they in turn say " Mutarim Lah- it is annulled".