I included this bit from a book by Tremper Longman III in our Psalms class notes. He is explaining, crisply and effectively, the three main types of Psalms and our relation to each of them:
The three most commonly occurring genres [types of psalms] are characterized by the emotion that they express. They are hymns of joy, laments, and thanksgivings. These three genres relate very closely to the life of the worshiper. When the Israelite was in harmonious relationship with God and his or her circumstances, he or she would sing hymns of praise to God. When God seemed distant and the worshiper experienced distress, a lament was in order. When the lament was answered, the Israelite responded with a song of thanksgiving. W. Brueggemann has helpfully categorized these three genres as songs of orientation, disorientation, and reorientation.