When Jesus walked the earth, he taught his disciples to baptize, he breathed the Holy Spirit on them, he reconciled people with God by forgiving their sins, he healed the sick, he honored marriage as an institution established from the beginning, he set apart certain disciples as apostles for a unique mission, and most importantly, he nourished them on the journey and bound his self-sacrifice into the Passover ritual meal of thanksgiving that he lived out in his life, death and resurrection. These seven grace-filled activities of Jesus have been carried on by every generation of disciples to the present day. We call them sacraments = actions that make visible the invisible grace of God.
It is true that Jesus did many other actions and that God can give us grace in any manner God wishes. However, the sacraments are unique moments in our life of discipleship for several reasons. Jesus did these actions, so we do well when we do them in memory of him. They give us certainty that God gives grace when we are obedient to the will of God. That certainty is consoling when we wonder whether or not what we are doing is the work of God or not. Jesus told us to "baptize all nations in the name of the Father, and of the Son, and of the Holy Spirit," and so we do. Likewise, every sacrament is an action guided by the Holy Spirit through today's apostles (Bishops) and their co-workers/assistants (priests & deacons), thus keeping a tie of apostolic succession from the early church to the present. Water, oil, bread & wine, and special formulas of prayer spoken by the minister of the sacraments are the outward signs of the inward activity of invisible grace that God is working.
Baptism: The person is immersed in water (or the water is poured over the person) as a sign that God is washing away sin, while the minister says, "I baptize you in the name of the Father, and of the Son, and of the Holy Spirit." In that moment, the person is adopted by the Heavenly Father, making him or her an adopted child of God. The baptized person also becomes a spiritual member of the Body of Christ and a member of the Catholic Church.
Confirmation: The bishop places his hand on the candidate's head while administering sacred chrism oil on the candidate's forehead, saying "Be sealed with the gift of the Holy Spirit," and acting as Jesus did when he breathed his Holy Spirit upon the apostles. Confirmation completes the initiation begun in baptism. The candidate is strengthened by the gift of the Holy Spirit to be able to carry out the works of discipleship as a fully initiated member of Christ's Body.
Reconciliation: The penitent person who has sinned in a serious way must repent and ask the Lord's forgiveness. In this sacrament, Jesus' words of forgiveness--I absolve you from your sins, in the name of the Father, and of the Son, and of the Holy Spirit. Amen-- are spoken by the priest after the penitent has confessed his or her sins. In the early church, penitents used to confess publicly before the community of faith, but nowadays the priest stands as representative of both Jesus and the Church in forgiving sins.
Eucharist: Many events of Jesus' life are incorporated into this sacrament--the feeding of the five thousand, the passover meal, the Last Supper, the crucifixion, the resurrection from the dead, and many other moments remembered within the words of the Eucharistic prayers--just to name a few examples. The priest prays over the bread and wine, invoking the Holy Spirit to act in power as Jesus' own words are recited. The bread and wine appear the same after the prayers, but their substance has been transformed into Jesus' self-offering to the Father, memorialized in the blessed sacrament but yet still a living sacrifice. We transcend space and time, ourselves attending the Last Supper, standing at the Cross, witnessing the resurrection. We believe Jesus is truly present to us in the Eucharist from that moment of consecration until the Body and Blood of Christ are received by us at communion time. The Eucharistic is the source of our faith, and it is the summit of Christian communion with God and one another.
Anointing of the Sick: In the letter of St. James we read, "If there are any among you who are sick, let them send for the priests of the church, and let the priests pray over them, anointing them with oil in the name of the Lord." The priest does just that, often visiting the sick, praying over them and anointing them with blessed oil. Always, the Lord heals something for the person, but sometimes He still performs miracles through the anointing, healing the person from physical ailments for a time. Most of the time, the sacrament is given when the person is close to death and in need of spiritual strength.
Holy Matrimony: The man and woman stand before God and the community, speaking their vows to one another, and entering into a partnership for the whole of life, for the good of the couple and the good of children. In doing so, the couple manifests the invisible grace of God's love, the Father loving his Son through the Holy Spirit, and vice versa. "I, N., take you, N., to be my wife/husband. I promise to be true to you in good times and in bad, in sickness and in health. I will love you and honor you all the days of my life." It also is a sign of the love of Christ for the Church, laying down his life for her salvation.
Holy Orders: The young man commits his whole life to the Lord for the sake of the Kingdom of Heaven. The fulness of Christ's powers are given to the bishop, who stands in the person of Christ the Head of the Body, carrying on the office of Apostle for a certain territory in the Church. To assist him, the bishop has priests and deacons. The priests help bring us the sacraments, especially Reconciliation and Eucharist. Deacons assist at the altar, proclaim the gospel at Mass, and make sure that the poor are cared for.
In short: Jesus saves us from sin in baptism, confirmation strengthens us by the Spirit, reconciliation repairs our relationship with God, eucharist nourishes us on the journey, anointing of the sick heals our body and soul, matrimony unites a couple so that they can raise children well, and holy orders sets someone aside so that we always have access to the sacraments when we need them.