CCC Article 2, 100 (Page 35): "The task of interpreting the Word of God authentically has been entrusted solely to the Magisterium of the Church, that is, to the Pope and to the bishops in communion with him." What exactly does this mean? What does interpreting the Word of God imply?
This means that the Magisterium of the Church is used to specify to the People of God and to the world how, exactly, the Word is to be applied to our daily lives:
The Roman Pontiff and the bishops are "authentic teachers, that is, teachers endowed with the authority of Christ, who preach the faith to the people entrusted to them, the faith to be believed and put into practice." The ordinary and universal Magisterium of the Pope and the bishops in communion with him teach the faithful the truth to believe, the charity to practice, the beatitude to hope for.
(Catechism of the Catholic Church paragraph 2034; the quote is from Lumen Gentium, section 25.)
This echoes and explicates paragraph 890 of the Catechism:
The mission of the Magisterium is linked to the definitive nature of the covenant established by God with his people in Christ. It is this Magisterium's task to preserve God's people from deviations and defections and to guarantee them the objective possibility of professing the true faith without error. Thus, the pastoral duty of the Magisterium is aimed at seeing to it that the People of God abides in the truth that liberates.
In other words, it is the task—the pastoral duty—of the Pope and the other bishops in communion with him to watch over their flocks, to ensure that what the People of God believe and practice is in accord with the Word of God as it appears in the depositum fidei, the "deposit of faith" given us by God through Jesus and the Holy Spirit. To do so, they must pray and think over what the Word means, and what it implies for Catholic life, so that they can pass on appropriate beliefs, practices, and teachings to the Church. This is the "interpretation" mentioned in the Catechism.