What is the Trinity? The term “trinity” is the doctrine that God exists as a unity of three distinct, simultaneous persons: the Father, Son, and Holy Spirit. Each of the persons is distinct from the other in relation (Economic Trinity), yet each is identical in essence (Ontological Trinity). The Trinity is not comprised of parts – as in the three persons being three parts of God. Instead, there is one being: God. We call this Divine Simplicity. God is one thing, one substance, one essence. Therefore, because there is only one God, there is only one will. Yet, from Scripture, we perceive the Trinity as three simultaneous and distinct persons: Father, Son, and Holy Spirit. Furthermore, the distinction of the persons is due to their relational properties (e.g., the Father begets the Son, the Son is begotten, and the Holy Spirit Who proceeds from the Father and the Son) without implying separation. 
“…the persons are identical in all things except their eternal relations of origin (personal properties): paternity, filiation, spiration. These and these alone distinguish the persons.” (Barrett, Matthew. Simply Trinity, p. 150. Baker Publishing Group. Kindle Edition.)
The Father is in a paternal relation to the only begotten Son, Jesus, John 1:18; 3:16. The Holy Spirit proceeds (spiration) from the Father and the Son (John 15:26; Gal. 4:6; Phil. 1:19). See What is the filioque clause controversy? Is it biblical?