"Honor paid to the saints [or martyrs, or Mary, or the Cross, or etcetera] who, by their intercession and example and in their possession of God, minister to human sanctification, helping the faithful grow in Christian virtue. Venerating the saints does not detract from the glory given to God, since whatever good they possess is a gift from his bounty. They reflect the divine perfections, and their supernatural qualities result from the graces Christ merited for them by the Cross. In the language of the Church's liturgy, the saints are venerated as sanctuaries of the Trinity, as adopted children of the Father, brethren of Christ, faithful members of his Mystical Body, and temples of the Holy Spirit".
Jesus is the only mediator between Men and God, but friends, clerics, or others, including saints, martyrs, or the Blest Virgin, may "pray for us" to Christ. Anyone, including the Blest Virgin, may be an Intercessor/mediator between Men and Christ, but Christ is the intercessor/mediator with the Father.