Confirmation strengthens baptismal grace through the gift of the Holy Spirit. It deepens union with Christ and the Church and strengthens a person to witness to the faith.
A little more context
It is not graduation from practicing Catholicism. The sacrament prepares a person for continued discipleship and service. The age and preparation process vary, and Eastern Catholic practice differs from common Latin Church patterns. Ask your parish which path applies to you or your child.
A practical beginning
Prepare with regular prayer, honest questions and participation in parish life. A sponsor can be a real companion during preparation and afterward. Choosing a saint, where that custom is used, is an opportunity to learn about a life of faith.
Source & further reading
Catechism 1302–1305: the effects of Confirmation (opens in a new tab)↗Teaching summaries are introductions. Follow the linked Church source for its fuller context.