OpenHistoricalMap has several resources for learning about the project, asking and answering questions, and collaboratively discussing and documenting mapping topics.
OHM Mailing List
Ask a question or discuss interesting matters on the OHM mailing list - sign up at the link above.
Join the OpenHistoricalMap channel for free-flowing chat about OHM, courtesy of some enthusiastic OHM users.
Browse the wiki for in-depth OHM information as well as very helpful OSM information, courtesy of the OSM Wiki.