http://www.mormonnewsroom.org/article/mormon-lay-ministry
The Church of Jesus Christ of Latter-day Saints functions in large measure because of the unpaid volunteer ministry of its members. In fact, this lay ministry is one of the Church’s most defining characteristics. In thousands of local congregations or “wards” around the world, members voluntarily participate in “callings” or assignments that provide meaningful opportunities to serve one another. It is common for Church members to spend 5-10 hours a week serving in their callings. Some callings, such as a bishop, women’s Relief Society president, or stake president may require 15-30 hours per week.
Callings in the Church are not sought after or campaigned for. Members are simply asked to be willing to accept assignments that come to them through Church leaders. These leaders seek inspiration through prayer about whom to call. Church members, for the most part, are willing to accept these callings.