The book of Psalms is a collection of 150 poems and prayers, written by some known and some unknown authors over a period of many years. We know a few writers, David being the most famous of them.
The 150 Psalms are subdivided in five different books. That is not a coincidence. The Pentateuch or the books of Moses (the Torah) are five books, the Psalms are in a way a reflection of the journey of God's people in the Torah.
The Torah starts with creation and ends at the border of the promised land. In the same way, the Psalms are meant to accompany you during the journey of your life.
We will look at the Psalms from a Christian perspective, as they speak of Jesus the Messiah and Christ Himself quoted them repeatedly (especially Psalm 110).