Why the congregation goes down during the Eucharistic Prayer.
Kneel after the Holy, Holy, Holy and remain kneeling through the consecration until the great Amen.
In the United States the faithful also kneel after the Lamb of God until they come forward for Communion.
Stand instead if kneeling is not possible. Health, pregnancy, age, and injury are reasons, not excuses.
Kneeling is the body admitting that it is not the biggest thing in the room. At the consecration the Church claims that Christ is made present on the altar, and a body that stays casual during that claim is quietly disagreeing with it.
The early Church prayed standing, especially on Sundays and in Easter season, because standing is the posture of the risen. Kneeling was the posture of penance and of weekdays.
As Eucharistic devotion deepened in the West, kneeling attached itself to the consecration and became the ordinary posture there. The Christian East still stands, and both are Catholic.
Because posture is discipline rather than doctrine, it varies by country. What your parish does is set by the bishops of your nation, not by preference.
Kneeling at the consecration is the norm where you live unless health prevents it or the church has no kneelers. There is no obligation to injure yourself for a posture.