The word tithe literally means a tenth part, most often in relation to a tenth part given to God. Just as tithing is commanded in the Bible; Abraham and Jacob as well as other ancient prophets paid tithes, (see Leviticus 27:32), the members of the Mormon Church also pay tithing of ten percent of their yearly income.
In a revelation given through Joseph Smith, the first prophet of the Mormon Church, the Lord taught how to properly give tithes. "And after that, those who have thus been tithed shall pay one-tenth of all their interest annually; and this shall be a standing law unto them forever, for my holy priesthood, saith the Lord" (see D&C 119). To Mormons, tithing is seen as giving only a small part of what is already God's. All that a person has is really the Lord’s; so giving a tenth part back is really not too much for the Lord to ask. Paying tithing in the right attitude is also a way that people can show their love for God and all that He has given them.
It is shown in several scriptures that blessings from the payment of tithing are both temporal and spiritual, and failure to pay an honest tithe is a form of robbery (see Malachi 3:8-12; Doctrine and Covenants 64: 23-25; 85:3,) In Malachi 3:10 it says, "Bring ye all the tithes into the storehouse, that there may be meat in mine house, and prove me now herewith, saith the LORD of hosts, if I will not open you the windows of heaven, and pour you out a blessing, that there shall not be room enough to receive it." In this verse it is obvious that the Lord promises blessings to those that willingly pay an honest tithe. "President J. Reuben Clark, Jr., a modern prophet, said over and over again that the Lord would never let one of his Saints who had been faithful in the payment of tithes and offerings go without the necessities of life" (see Marion G. Romney, “The Blessings of an Honest Tithe,” New Era, Jan.–Feb. 1982, 45). Members who faithfully pay tithing are promised spiritual blessings as well. "I think it is not well known in the Church that payment of tithing has very little to do with money. Tithing has to do with faith"(A. Theodore Tuttle, in Conference Report, Apr. 1970, 86).
Tithing is used to help maintain and build up the Church. After it is given to the bishop, the congregation leader, it is sent to the Church headquarters. Then it is combined with other tithes and distributed to pay for building and maintaining temples, meetinghouses, and other Church property. It is also used to pay for printing books, and other materials that are used to teach the gospel. Some of it is also used to help support missionaries and family history work.ru:Десятина