The Rite of Christian Initiation of Adults (RCIA) is not a Sacrament but rather the name of the process of preparation for adults to receive the Sacraments of Initiation. It involves meeting regularly (usually from Autumn until Easter) with the priest and other Catholics to learn about and experience Catholic Christian life and community. During Lent, there are special moments of prayer to be celebrated and the Sacraments of Baptism, Confirmation and Eucharist are often given at the Easter Vigil of the Resurrection of the Lord.
If you are interested in becoming Catholic or completing your sacraments as an adult, please speak to your Parish Priest.