At its core, conversion requires that the ger (convert) willingly, and without ulterior motive, accept kabbalat ol mitzvot - the acceptance of the mitzvot (commandments) upon him or herself. The classical sources say that, once this intent has been shown, he/she has to be taught a few "light" commandments and a few "heavy" commandments, and then they are ready to convert.
In modern times, this early stage has become quite involved. Although it varies greatly, based on the Rabbi, and the specifics of the case, conversion often takes a minimum of a year, and often quite longer. It involves education about the basic tenents and practices of Judaism, a chance to learn first-hand about Judaism by participating in Jewish life (one of the reasons for the year of study is to ensure that the ger has experienced all of the Jewish holidays, personally), as well as a chance to explore larger philosophical issues (such as theology) with the sponsorong Rabbi.
In Reform Judaism, there is also a major difference with the idea of kabbalat ol mitzvot. Unlike Orthodox and Conservative Judaism, Reform Judaism doesn't demand obedience of all Jewish laws; it instead insists on learning about those laws, and being guided by them. Most Reform Rabbis would insist on some serious level of observance before they would convert someone, but few would demand that any specific practices, such as keeping kosher, be adhered to.
The details of this preparatory period vary widely from movement to movement and, especially, from Rabbi to Rabbi. the only way to really get an idea of what is involved is to make an appointment with a Rabbi and ask him or her.
Once the candidate is ready for conversion, they are brought before a beit din, a Rabbinical court. This beit din ensures that the ger is ready for conversion (both in terms of sincerity, as well as general preparation for a Jewish life), and then (hopefully) accepts the ger ito the Jewish world. But, the ger is still not a Jew, at this point.
Once accepted by the beit din, the ger becomes a Jew by undergoing a ritual or two. Men are required to have a brit milah - a ritual circumcision. Men who were already medically circumcised instead go through hatafat dam brit - the ritual drawing of a drop of blood from the circumcision site. Both of these rituals officially bind the man to the brit (covenant) with God. The final stage of conversion, for men and women, is immersion in a mikvah - a ritual bath. Once that ritual is performed, the ger is now a Jew!
Again, in the Reform movement, standards vary. Some Rabbis insist on brit milah or hatafat dam britand mikvah; some don't. The only way to be sure is to find a Rabbi, and ask!
From an Orthodox perspective you need to see yourself as a Jew and not as part of any other religion. You need to know how to be observant on a day-to-day basis and to be observant in that way.
I would suggest you resubmit your question here so a Reform and Conservative Rabbi can answer for their movements, but in general, the Orthodox community requires significantly more practice of traditional observance than the other movements. For more on the Orthodox perspective, see the website of the Rabbinical Council of America.
Answered by: Rabbi --- Not Active with JVO Suspended
To convert under the auspices of a Conservative Beit Din (rabbinic court), the interested individual must:
1) Engage in a course of study with a Conservative rabbi or in a community course that adheres to the Conservative rabbi's study requirements. The length of study varies from community to community but is often between six months and one year. This curriculum also varies but often includes studying: the Jewish holidays, life cycle rituals, the Jewish approach to Bible study, the Oral Torah, Halacha and Conservative theology.
2) After this course of study, the person interested in converting meets with a Conservative Beit Din which consists of three Conservative rabbis who ask him/her questions which can range from biographical information and a short description of this person's journey to Judaism and questions about what he/she learned during his/her course of study. They may also ask what mitzvoth the person has already “taken on” and which he/she see himself/herself working toward.
3) A male convert must undergo a circumcision if he is not circumcised. If he has already been circumcised then hatafat dam is required. In this situation the mohel pricks the penis to draw a small amount of blood. Immersion in the mikvah follows.
4) A female convert must immerse in the mikvah.
These are the basic requirements. Some rabbis have the convert return to the synagogue following immersion to say the Sh'ma in front of the open Aron Kodesh holding the Torah and/or give him/her an aliyah to the Torah on the Shabbat following the conversion. However, this is a matter of personal custom on the rabbi's behalf and is not a requirement.