It's a charter stating that God has called this group together for certain purposes. The constitution includes bylaws that determine the procedures by which the church is to be governed. After the constitution has been drafted and incorporators and registered agents have been selected. The church then receives a certificate of incorporation. You may need to provide a copy to your county's recorder of deeds.
Some denominational offices have sample bylaws that can be adapted to local congregations.
You could use the bylaws of a well-administered church as an example. Samples of nonprofit bylaws can be found in How to Form a Nonprofit Corporation in All 50 States. You can hire an attorney to write the bylaws, but that will be costly. Make sure an attorney reviews bylaws before implementation. A vote of the incorporators plus the entire congregation, if desired, will activate them.