after discerning your primary vocation, marriage, and then discerning your career path or profession, you can also work in that profession in service to the Church. You can serve Either as an employee of a diocese, parish, school, hospital, social service agency or other Church institution, or as a volunteer. For instance the Church relies on lay businessmen with both expertise in finances, development, risk management, investments etc. and Catholic values to help care for the temporal property of the Church. Administration is one of the charismatic gifts so those endowed with such gifts should use them to serve the Church. Same with teaching and the other service gifts.
The most important task of the laity of course is building up families, the domestic church.