Question:
What is the Holy Spirit? 

Answer:
1288 "From that time on the apostles, in fulfillment of Christ's will, imparted to the newly baptized by the laying of the hands, the gift of the Spirit that completes the grace of Baptism. For this reason in the Letter to the Hebrews the doctrine concerning Baptism and the laying on of hands is listed among the first elements of Christian instruction. The imposition of hands is rightly recognized by the Catholic tradition as the origin of the sacrament of Confirmation, which in a certain way perpetuates the grace of Pentecost in the Church"  

Catechism of the Catholic Church

The Holy Spirit is a Person, not a force. The divine persons do not "share" the one divinity among themselves, but each of them is God whole and entire. "God is one but not solitary." The divine persons are distinct from one another, but are relative to one another. Because it does not divide the divine unity, the real distinction of the persons from one another resides solely in the relationships which relate them to one another. "While they are called three persons in view of their relations, we believe in one nature or substance."
  

From AskACatholic.com