The majority of the work in the Office of Canonical Affairs revolves around the Diocesan Tribunal (Church Court) and the adjudication of petitions for declarations of nullity for those who wish to remarry in the Catholic Church. These declarations of nullity are more commonly referred to as “annulments.”
Any persons having presented themselves to others as married, are presumed to have been married as the church understands. (See link The Church’s Understanding of Marriage) For that reason, any person having been married before must petition to a Church court to have the previous union investigated to see if there is a reason why the exchange of vows did not constitute valid matrimonial consent. Divorce in itself is a termination of the "civil union" of the couple; even then, in the Church's understanding, parties are still married under Divine Law. For this reason, if a divorced person enters into a subsequent civil union, they remove themselves from the Sacraments (but not the Church). Otherwise, a divorced Catholic who has not remarried may continue to receive the Sacraments.
Once an investigation shows there was not a valid consent according to Church Law, a Decree of Nullity is issued. No Church marriage is allowed unless and until a Final Affirmative Decree has been obtained. Since there is no set time for the process and there are no assurances of an affirmative decree, no date can be set for a Church wedding until a Decree of Nullity has been issued by the Tribunal.
Either of the two parties of a previous union can petition the Church to consider declaring the union as not valid under Church Law. A union not valid under these conditions is considered "null", i.e., there was not a valid consent. The Catholic Church's declaration of a marriage being "null" has no effect on the status of the union under Civil Law nor does it have an effect on the status of Children of the union. An individual "petitions" the Church court in the diocese in which they live; if the petition needs to be handled elsewhere, the local Tribunal will assist in initiating the process. In the Diocese of Boise, each petition is started with assistance of trained advocates in the local parish. Any priest, deacon, or trained lay advocate in the Diocese of Boise can provide this assistance.