Trinity can be thought of as “three in one.” It is used to reflect the nature of God. There is one God, with three distinct parts: the Father (creator), the Son, Jesus (savior), and the Holy Spirit (counselor and guide).
This three-fold nature of God can be better understood by comparing it to water, which also exists in three forms or states: solid (ice), liquid (also called water), and gas (steam or vapor). Each is still water, but each is manifested in a different form. The same holds true for God.
An alternate analogy is to consider an egg: there is the shell, the white, and the yolk. Each part is different, yet each is still an aspect of an egg. So it is with the three parts of God.