One of the most significant works of the Holy Spirit occurs at every Mass. Did you know that every time you attend Mass, you can see a miracle performed by the Holy Spirit on the altar. It occurs when the Priest places his hands over the bread and wine on the altar and prays an invocation to the Holy Spirit. Here is the text from the Second Eucharistic Prayer during Mass.
You are indeed Holy, O Lord,
the fount of all holiness.
Make holy, therefore, these gifts, we pray,
by sending down your Spirit upon them like the dewfall,
so that they may become for us
the Body and Blood of our Lord Jesus Christ
—- Catholic Eucharistic Prayer
The U.S. Conference of Catholic Bishops (USCCB) website describes this part of the Eucharistic Prayer at Mass, called the Epiclesis.
c) The epiclesis, in which, by means of particular invocations, the Church implores the power of the Holy Spirit that the gifts offered by human hands be consecrated, that is, become Christ’s Body and Blood, and that the unblemished sacrificial Victim to be consumed in Communion may be for the salvation of those who will partake of it.
— U.S. Conference of Catholic Bishops
Beyond the Mass, you can also see the Spiritual Gifts of the Holy Spirit (Fruits, Gifts, and Charisms) active in people you encounter each day.