Complex sentence: Non-stipendiary ministers or non-stipendiary priests (NSMs) are religious ministers who do not receive payment for their services, and who usually have alternative employment which provides monetary income with which they can support themselves.
Split into simpler sentences: Non-stipendiary ministers or non-stipendiary priests (NSMs) are religious ministers who do not receive a stipend (i.e. payment) for their services. They usually have alternative employment which provides monetary income with which they can support themselves.