About The Traditional Latin Mass
As you enter the church for the Latin Mass, you may notice a quiet, prayerful atmosphere. This results in large degree from the tone of the Traditional Latin Mass (also known as Mass in the Extraordinary Form) itself. Many of the prayers of the TLM are recited by the priest in a low (inaudible) tone. This helps to foster a spirit of prayerfulness and meditation during the Mass. It will also be evident to a newcomer that the priest almost always offers the TLM ad orientem; that is, toward the Liturgical East. For Catholic Christians have longed believed that Christ Our Lord will rise in the eastern heavens on the Last Day, just as He ascended: “Men of Galilee, why stand ye there looking into the heavens? This Christ will return to you as you have seen Him leave…”
Entrance of the Church
At the entrance to the Church, it is customary for Catholics to sign themselves with the Sign of the Cross after they have dipped their fingers into the Holy Water font. This reminds us of our Baptism, which just like the door which is the entry into the church, so also Baptism provides our entry into the life of sanctifying grace, which is our pledge, and our participation already, in eternal life.
Also, at the door of the church, you will find little red pamphlets that contain the basic prayers of the Mass in Latin on one side, and the on the other side are the same prayers in English. The pamphlets have the prayers that are common to all Masses (the ordinary parts) and some proper prayers for a particular feast. However, some people have their own missals that have not only the ordinary parts, but also the proper prayers for each particular Mass. But the red pamphlets are a good starting point for newcomers to the TLM.
Inside the Church
Before Catholics enter the pew, they genuflect to the Christ Almighty in the Tabernacle. The Tabernacle contains consecrated altar breads called hosts or the Blessed Sacrament. Through the mystery of transubstantiation the hosts, while retaining the appearance of bread, have been substantially changed into the Body and Blood of Jesus Christ. This Real Presence of Christ remains after Mass and always until the Hosts are consumed, and therefore the Blessed Sacrament is reserved in the Tabernacle for the devotion of the faithful and for those who are sick or dying.
Traditional Latin Mass: Postures
There are basically three postures to be observed during the TLM: kneeling, sitting and standing. This PDF link will provide a guide that can be printed out, or you can used the notes in the margin of the red pamphlets. Kneeling is observed for a generous portion of the TLM, but those who with physical impairments should not feel constrained to kneel.
Traditional Latin Mass: Important Moments
The most important moments of the Mass are the Consecration and the Communion Rite. At the Consecration the priest utters the prayers that were spoken by Our Savior Jesus Christ at the Last Supper and which affect the transubstantiation of the bread and wine into the Body and Blood of Christ. This is truly the most solemn moment of the Mass and calls for quiet attention, adoration and a reverential fear of the Lord. At this moment, the bells are rung by the Altar Server to alert all the faithful to the importance of the moment.
Very closely associated with the Consecration is the Holy Communion. Those who are properly disposed to receive the Blessed Sacrament (that is, Catholics having fasted for the required hour before receiving and not being prevented from receiving by any objective condition of mortal sin), may approach the Altar Rail and kneel as a space opens up. To receive Holy Communion, one simply extends the tongue while resting the tongue on the bottom lip and opening the mouth to receive the Sacred Host. Afterwards you may make the Sign of the Cross, and you may wish to linger at the Rail for a brief moment with your eyes closed in Thanksgiving. Having returned to your pew, you will have the opportunity to continue to kneel and pray in Thanksgiving.
Dress at the Traditional Latin Mass
A final word about dress at the Traditional Latin Mass. Whenever Catholics attend Mass, it is fitting that they dress modestly and in a manner suitable for the occasion. One should avoid coming to Mass in attire that is physically revealing, vain or especially casual. “It is always most edifying to note that gentlemen wear a coat and tie to Holy Mass. Going back to the tradition of the early Church, many women, in imitation of the Blessed Virgin Mary, choose to wear the chapel veil (i.e. mantilla), as a way of expressing their modesty and femininity.”
More tips can be found here: https://sanctamissa.org/en/faq/newcomers-to-the-traditional-latin-mass.html