The most thorough "textbook" on the role and work of the Holy Spirit that I've come across is "Your Life in the Holy Spirit" by Alan Schreck. This is a revision of his earlier work "Hearts Aflame". For anyone interested in the Charismatic Renewal, this book clearly explains who the Holy Spirit is, what He does, how he helps us, and how He guides the Church.
This explaination of glossolalia (speaking in tongues) is the clearest I've found anywhere:
The authentic gift of glossolalia or speaking in tongues is twofold. First, just as the genuine gift of healing or working miracles, it requires God's action. Second, glossolalia requires a gift of faith to be recieved and exercised. God does not force anyone to speak in tongues; he does not force anyone to engage in any particular form of prayer. The person praying must "step out in faith" and yield to the gift, making sounds to allow the language of prayer to come forth.
Admittedly, speaking in tongues requires faith and an unusual degree of humility (at least for the "sophisticated" people of the twenty-first century who often have difficulty becoming like little children to receive a simple gift). Also, many people reject it simply because they do not understand it or fail to realize how it could benefit them.
And yet, even something as simple and apparently unnecessary as speaking in tongues serves to show the power and goodness of God's gifts through the Holy Spirit. It truly is a gift for those of us who "do not know how to pray as we ought" (Romans 8:26). Glossolalia is particularly helpful when words cannot easily express certain interior states, such as the heights of joy in praising God for his goodness, or the depths of sufering or sorrow.
Some Catholics may be tempted to limit their prayer to formal prayers or to the Mass and decide that glossolalia is not for them. And if Pentecost had not happened, then glossolalia--along with mysticism, or contemplative prayer--might well be seen as unnecessary, extraordinary, or outmoded. But in fact, Jesus completed his saving actionby sending us the Holy Spirit at Pentecost, and the Holy Spirit is always ready both to do new things and to renew the old and forgotten things that we find in Scripture and in our tradition!
~Alan Schrek, Your Life in the Holy Spirit (Word Among Us Press, 1995)