A saint is someone in Heaven. A small percentage of the saints are canonized, that is, officially recognized as saints and held up for the whole Church to honor as such, but simply because the Pope has not canonized someone does not mean that the person is not a saint. Saints are important to Catholics for at least three reasons: we honor them; we imitate them; and we ask for their prayers.
When we honor the saints, we are honoring God’s works of art. Each one of us is called to reflect a certain aspect of God’s truth, goodness, and beauty. The saints are those who, because of God’s grace, now do that in Heaven without sin or imperfection. The goodness we honor in the saints is the goodness that God put there, just like the beauty of a painting or a statue was put there by the artist who made it. If we did not honor the saints, it would be like going to an art gallery and complimenting the artist while ignoring all of his works. We give thanks to God for the beauty and goodness of the universe, plants, and animals, so how much more should we give him thanks for the great things he has been able to do in the lives of human beings who are made in his image! The Bible tells us that God himself honors the saints (Jn 12:26)!
Catholics also try to imitate the saints, not in an outward manner (e.g., by dressing like them) but in an inward manner by trying to imitate their virtues. The saints are real people who struggled with the same problems that you and I do. When we find a saint who lived in similar circumstances to us or who had to grow in some of the same ways that we do, it is very helpful for us to study the life of that person. They show us that it is really possible to follow Jesus. They help show us the way. They inspire us by their example. Again, the Bible tells us that we ought to imitate the saints (e.g., 1 Cor 11:1).
Catholics should also try to foster a relationship with some of the saints. The saints are friends of God, and any friend of God should be a friend of ours! It is silly to think that those who are now closest to God are separated from the Church. Nope. The Church is the Body of Christ, and so the closer we are to Christ, the closer we are to one another (Eph 4:25). The saints are ready to help us who are still struggling in this life. They pray for us, and they present our prayers to God (Rev 8:4). Sometimes, we treat God’s Church more like a government bureaucracy than a family: We think that it’s easier or more efficient to go “directly” to God without involving the saints. This is really kind of silly, since the point of prayer is not to make our requests known to God, who knows them already (Mt 6:8), but rather because God wants us to be in communication with him and to learn to submit our wills to him. The saints don’t get in the way of this process. God also wants them to be involved, since he wants us to pray for one another (Jas 5:16). Prayer is not about finding the easiest or most efficient way to get things done; prayer is about growing in intimacy with God, and the saints are part of God’s family like we are.