Words affect reality. Most people remember words spoken to them which profoundly affected. Words can affect reality. 
When a policeman lays hold of someone and says, 'You are under arrest', reality changes. The person in question had been a free citizen just a moment before. But now he or she is in the custody of the State. 
God's words do not merely affect reality, but can create reality. In the book of Genesis, when God says, 'Let there be light', light is instantly created. 
John 5 recounts how Jesus met a man who had been crippled for 38 years. The Lord Jesus says, 'Get up, pick up your sleeping-mat and walk', and immediately he is healed and starts walking. 
Likewise, at Mass when the priest speaks in the person of Christ saying, 'This is my Body', reality changes. The appearance remains the same but the reality is now the Body and Blood, Soul and Divinity of Jesus Christ. This faith is based on the words of Jesus Himself. (The image is a depiction of the Institution of the Eucharist)

Fr Robert Barron gives some great insights on the Real Presence of Christ in the Eucharist in this clip: 

The coming of Jesus Christ brought the revelation that God is a trinity of Persons. It means that God is not a lonely figure living like a recluse. 
Instead, divine life is an eternal exchange of love of the Father and the Son and the Holy Spirit. 
A common misunderstanding about the Blessed Trinity is that it means that there are three gods. It has been revealed that there is one divine Nature but three divine Persons. 
There is a distinction between person and nature. Each Person is not a separate god. The blessed Trinity is a mystery but not illogical - only above reason.

The following sketch may help to understand some of the terms:

The Holy Spirit can bring many varied images to mind. One could imagine an ethereal ghost character who floats here and there visiting people. Or one could imagine an impersonal force for good.
The bible employs varied symbols to disclose the mystery of the Holy Spirit. Important symbols of the Holy Spirit include fire,  anointing and a dove. 
The Lord Jesus communicated the Gift of the Holy Spirit to His Apostles after He rose from the dead. Jesus reveals that the Holy Spirit is a Person. The Holy Spirit is the third Person of the Blessed Trinity. 
He reminds us what Jesus taught and bears witness to Jesus (cf. John 14:26, 15:26). The Holy Spirit can renew our souls and minds.
 He can help us to pray (cf. Rom 8:26) and desires to bring us to deeper communion with the Heavenly Father and the Son. We can always pray the simple words, "Come, Holy Spirit". (Image is depiction of Pentecost)

In this funny clip Chris Padgett teaches about the Holy Spirit: