The Book of Psalms is a collection of 150 ancient songs. King David wrote many Psalms (that is, songs).
There are many different subjects. Many Psalms are glad songs which praise God (for example, Psalms 103 and 150). Other Psalms are sad prayers (Psalm 74). Some Psalms explain that God will rescue us from our troubles (Psalms 40 and 41). And some Psalms are about the history of Israel (Psalms 74 and 78). Psalm 119 is about the Bible. In Psalm 51, David confesses an evil deed. Psalm 22 describes how Jesus would suffer. Psalm 2 tells us that God will rule the world. Psalm 1 teaches that we must love God.
The Psalms are a very special part of the Bible. We can learn many things about God from their beautiful words. They are in the Bible's Old Testament.