What is teshuva for non-Jews? I'm Christian and have broken some laws of Noah, so does praying for forgiveness as a Christian and not doing the sin constitute teshuva for me? Or is just feeling regret and not doing the sin again considered teshuva?
First of all, to clarify, I am not a Rabbi.
In your post you say you are a Christian and you have broken some of the laws of Noah and you would like to know what exactly tshuvah (repentance) means for you.
I will do my utmost best to explain what tshuvah means for us Jews (based on the knowledge I have received from my rabbis) and I believe it is applicable to Gentiles as well. What I have learned is first of all tshuvah is not guilt. Tshuvah is repentance. The purpose of tshuvah is to rectify what you have done wrong and to get closer to G-d by using this as a step for growth. While it is sometimes a guilty feeling that brings people, that is not what tshuvah is and what I have learned is that the first step in tshuvah is letting that guilty feeling go as guilt does not promote growth because it brings on feelings of despair and is counterproductive to what we are actually trying to achieve (getting closer to G-d).
On a practical level this is what I have learned that are the steps of tshuvah:
Understand that we have done something wrong
Understand that we have done is done and now we have to fix that and self guilt is not the proper way to fix it
In our own words apologize for what we have done
Ask G-d to forgive us
Make a commitment not to what we have done ever again
Ask G-d to help us honor that commitment by helping us from above
Ask that the connection between G-d and you becomes stronger and that this experience will be used to strengthen the connection between G-d and you.
That is what I learned tshuvah is and I believe it can be easily applied for a Gentile.
Answered by הנער הזה excerpted from one of the links that AA gave in comments
Non-Jews are certainly able to do teshuva and be forgiven, as evidenced by the story of Jonah and Ninveh (who were forgiven, despite having sinned both against man and God). The Mabit, in Beis Elohim Shaar Teshuvah chapters 13-14 writes that although non-Jews are able to do teshuva, their repentance is fundamentally different than that of Jews in several important ways. However, all of the differences that he lists are metaphysical differences (such as not being forgiven right away, or not being able to exempt themselves from punishment in the afterlife). Regarding the actual procedure of repentance, however, it appears that Jews and non-Jews are equal in this regard. This is also borne out of the fact that the Gemara (and many later poskim) learn laws regarding the teshuvah of Jews from the story of Ninveh as it's portrayed in the book of Jonah (see Taanis 15a, for example).
Thus, just as a Jew has to be forgiven by his fellow who was the subject of his wrongdoing, a gentile must also be granted forgiveness from the person whom he has wronged before being forgiven by God. The "release clause" that is included in the pre-Yom Kippur prayer may not suffice for anyone, Jew or non-Jew. This issue is discussed at length in this teshuva from R. Binyamin Zilber. However, given that it does work for Jews, it's possible that the original intent of the prayer is to only refer to Jews. Having said that, if you as the person reciting the prayer have in mind to forgive the non-Jews as well (and, better yet, if you say that explicitly), then whatever power it has for Jews is probably just as effective for non-Jews too.