I have some experience building communities in more technical audiences, but the principles are similar across audiences. Fundamentally, people are attracted to communities that provide them a sense of belonging (though attracting others with similar interests) and provides them with helpful information, either from writers or from the community. Once those key criteria are met, there are some ways to accelerate community growth, and then the "building" and "managing" become nearly indistinguishable.
However, as Lucas said above, the answer to your broad question is difficult to summarize! Hopefully at least that little bit of a tip helps.