We have here a new Psalm writer. His name will come up a few more times before we finish the Psalms. All the Bible says about him was that he was a "singer of Psalms" and appointed by David to be a singer. What does that mean? It means he probably was a Levite who had a great singing voice and David appointed him to be in charge or involved in the worship of God. His sons (or descendants) are also mentioned in several Bible places and apparently, they too were appointed as singers.
So what is this Psalm about? It is another accountability Psalm, just like the last one. The last Psalm (#49) was focused on people who cared more about money than God, this Psalm focuses on believers and discusses what God expects from believers. The later part of the Psalm then has a few warnings for nonbelievers, but most of it focuses on believers.
If I had to summarize this Psalm in one key thought, it is, "When we worship God, He doesn't just want us to go through the motions of worship, He wants us to put our heart into it and think about the things we are doing for Him." In other words, if we are grateful for His salvation we should act like we mean it.
When we are praying or doing things for others, we should not do such things out a sense of guilt, but do them out of gratitude for what God has done for us.