As others have stated, the Latter-day Saints that you are talking to are not representative, nor are they being told by “the Church” to say what they are saying. As a Latter-day Saint, I am comfortable saying that I wear garments to those that ask about it, and that they remind me of the covenants I have entered into with God. I don’t discuss specifics about them, beyond saying that they are white, consist of a shirt and bottom, and have symbols on them that remind me of various things related to the Gospel of Jesus Christ.
As far as specifics about what goes on in temples, there is a great deal that we often freely talk about about what goes on in temples of The Church of Jesus Christ of Latter-day Saints. Much of this can be found in various Church related publications. For example, I am comfortable saying that in a temple marriage, the couple kneels at an altar facing each other and are married “for time and all eternity”. In baptism for the dead, we stand in the baptismal font, and are baptized “for and in behalf of” deceased persons to offer the blessings of baptism to them (to accept or reject). In the Endowment, we are instructed on various aspects of the Gospel of Jesus Christ, beginning with the Creation, the Fall. In most temples, this includes the use of video. We enter into various covenants, put on ceremonial clothing, and at the conclusion, we pass through a veil in to the Celestial Room, entering into the presence of God. There is a prayer circle where we stand around an altar in ceremonial clothing and pray for the sick. The Encyclopedia of Mormonism entry on “Endowment” goes into this a little further. In the Endowment, we also covenant not to reveal specific things that we are taught, and those things are what we should not talk about, except within the temple walls. Some Latter-day Saints extrapolate this into meaning we really can’t talk about anything that happens in the temple, beyond saying we do eternal marriages, endowment, washing and anointing, etc. That is there own personal view, however not all Latter-day Saints will limit themselves to that, and they are not wrong for doing so.
Hope that helps.