Catholic children used to be taught, via the Baltimore Catechism, that "a Sacrament is an outward sign instituted by Christ to give grace". In The Power of the Sacraments Sister Briege McKenna talks about the sacraments as being food for our spiritual life. She takes each of the seven sacraments, talks about it being an encounter with God and gives examples of how that sacrament made a difference in someone's life. I love the way the book is filled with stories of real people touched by the power of God.
The Power of the Sacraments is a short book; I read it in less than an hour, but if you are wondering what the sacraments should mean for your daily life, I recommend it.