Psalm 104 is on God's greatness in the creation of the universe and its fullness. As used here, the fullness includes all things in the universe. Concerning God's greatness in creation, verse 24 says, "How many are Your works, O Jehovah! /In wisdom You have made all of them;/The earth is full of Your creatures."
Another part of God's history is narrated in Psalm 105. This psalm speaks of God in His dealing with Abraham and his descendants according to His covenant.
Psalm 106, the last psalm in this group, is on God in His dealing with Israel in the wilderness and in the promised land with His favor according to His covenant.
The praise of Jehovah in Psalms 103 through 106 issues in hallelujahs. These hallelujahs begin in 104:35 and continue in 105:45 and 106:1, 48.