@jewishorthomum thanks for OKing the new thread, and for doing the first one😀
@Fink I'm going to do a general roundup on conversion which hopefully answers you too.
For Orthodox Jews, conversion is allowed but not something we actively go out and encourage others to do. As the first thread explained, there are several reasons for this. You can convert, but it is not an easy process.
Converts have existed throughout Jewish history, and are very much seen as following in the footsteps of Avraham and Sarah. We are supposed to be treated with love and respect, and there are rules about shaming a convert or reminding them of their past. (Jews are not perfect, and sadly this is one Jewish standard that people sometimes fail to live up to).
These days, conversion is a 'way in' to the Jewish community for those not born to a Jewish mother. Some do it simply on principle, because we felt called to. Some are in a relationship or already married to a Jew and want to convert for their partner's/family's sake. Some have a Jewish father or other ancestry and want to make sure they are fully accepted as part of the Jewish community. And in some cases a person can't fully prove their Jewish status (kinda like losing their passport, I guess?), and go through a conversion to regularise their status - this is usually kept to the ritual itself if they are already fully observing Jewish practices like Shabbat, keeping kosher etc.
You need to apply to a Beth Din or religious court, who will oversee the process. The thing about 'turning away three times' these days is really just a guideline - it's not set in stone. The first time I wrote to the Beth Din, I got a standard letter which could be paraphrased as 'Orthodox Jewish life is hard and Jews have been persecuted a lot. Are you sure you want to do this?'. After the second letter, I was invited for interview and accepted onto the process. It took 2 years to complete (which is the quick end) BUT by that point I had been living a Jewish lifestyle for nearly 10 years and was 90 per cent of the way there when I started.
During the process, men are tutored by men and women by women (generally 1 on 1 in the UK). Men and women are also expected to have a Rabbi who will sponsor them through the process and be their port of call for questions during and after the process. This is because an important part of conversion these days is integrating into an active Orthodox community, and part of that is having a (professional) relationship with at least one Rabbi for guidance.
The Beth Din will decide when you are ready to go through the actual conversion ritual which makes you Jewish. This is circumcision (men only), immersion in a mikveh (men and women), and a commitment to take on and keep the Jewish commandments (mitzvot). Part of showing this commitment is making a verbal declaration out loud in the mikveh just before you immerse. The entire ritual is done in front of the Beth Din (women have something covering them for modesty!).
Post-conversion, for all practical purposes a convert is like any other Jew and should be treated as such. However, there are some specific laws which only apply to converts. Socially, depending on their background converts may also have additional challenges fitting into the community and navigating life events (which is why integration is so important).
I think the question about a Kohen (male) not marrying a female convert was answered in the first thread. Tbh it's a very difficult question to answer but if a follow-up is needed I will try.