In the Church, an ordinance is a sacred, formal act performed by the authority of the priesthood. Some ordinances are essential to our exaltation. These ordinances are called saving ordinances. They include baptism, confirmation, ordination to the Melchizedek Priesthood (for men), the temple endowment, and the marriage sealing. With each of these ordinances, we enter into solemn covenants with the Lord.
All of the saving ordinances can be performed in the temple, and indeed are performed there. The ordinances of temple endowment and the marriage sealing are done for for the living as well as for the deceased in the temple. The other saving ordinances are performed for the living within our regular church buildings, but they are performed for the deceased in temples.
I've spent my lifetime reverencing and loving temples and the ordinance work that we do therein. I look forward to talking a bit more in-depth about each ordinance in the next few days.