While it is true that not every book of the Bible was intended to be taken literally by the sacred writers, that does not mean that what is written does not describe real events that happened to real people. For example, in Genesis, we can be assured that we had original parents who were created by God with special grace. Our first parents fell from that grace by disobeying God; thus the grace they lost, we could not inherit. Did they literally eat fruit from the forbidden tree, or does that act symbolize something else? Does it matter what the sin is, or is the important thing to know that God forbade something, our first parents did what was forbidden with full knowledge and consent, that we are born with the effects of that original sin, which is a lack of sanctifying grace, and that while in sin, God gave them hope of restoring what was lost?
The Catechism explains:
Among all the Scriptural texts about creation, the first three chapters of Genesis occupy a unique place. From a literary standpoint these texts may have had diverse sources. The inspired authors have placed them at the beginning of Scripture to express in their solemn language the truths of creation - its origin and its end in God, its order and goodness, the vocation of man, and finally the drama of sin and the hope of salvation. Read in the light of Christ, within the unity of Sacred Scripture and in the living Tradition of the Church, these texts remain the principal source for catechesis on the mysteries of the “beginning”: creation, fall, and promise of salvation (#289).
I recommend that you read the Catholic Answers tract “Adam, Eve and Evolution” at our web site:**