This varies from place to place and rabbi to rabbi. Most larger cities have a community class.
Smaller cities rely on the rabbi.
In any case, contact the rabbi at your congregation or a local congregation. If there is no rabbi contact the local congregation and they will put you in touch with someone. If you need help, or are unsure about walking into the synagogue, there are some rabbis on the net who will be glad to talk to you about this important step. Rabbi Sherwood is Past President of the San Fernando Valley Interfaith Council, and has been an adjunct professor at St. John's Roman Catholic Seminary teaching a graduate course on Judaism to men studying for the priesthood. He is also the author of a curriculum for Introduction to Judaism.