A psalm is a hymn of praise intending to be sung to a musical instrument. The Biblical book of Psalms is a collection of 150 of these hymns. The reader does not need to read them in order, they are each a stand alone song or poem.
It seems the collection of the psalms was made by a number of people over a long period of time.
Psalm 1 is really an introduction to the whole collection. It shows the life of the godly in contrast to the life of the ungodly.