Salvation, in Roman Catholicism, is a process with many steps: Actual Grace, Faith, Good Works, Baptism, Participation in the Sacraments, Penance, Indulgences, and Keeping the Commandments. Basically, salvation is attained through baptism and good works. It is maintained by good works and participation in the sacraments. If lost, it is regained through the sacrament of Penance which only a Roman Catholic priest can administer. Add to this purgatorial cleansing after a person dies, and you can see that salvation is an arduous process.
In Catholicism, a person can gain salvation and lose it many times depending on the number of sins committed, their severity, and how much of the sacraments they participate in--in order to regain grace which enables them to do good works by which they are justified. Furthermore, justifying grace is infused into the Catholic upon baptism and via the sacraments. This grace can be gradually lost through venial sins or forfeited all together with mortal sins.