Lyrics are the words that ride on the melody of the song. They are the words used to express the ebbs and flows of the melody. They are the words used to communicate the theme of the song to the listener.
Now, the lyrics of every song will have an over-arching theme. This theme (most of the time) will be embedded or encapsulated in the chorus. The verse(s), will serve the purpose of expounding on that theme i.e going into more detail or explanation. Your next question might be "How do I decide on a theme?" Thankfully, as Christians the Bible is a one-stop shop for not just themes but also the lyrics required to express those themes. For instance, you just repented of a conscious sin you committed and you're remorseful and contrite so you want to sing about God's mercy/forgiveness and restoration. The book of Psalms provides a lot of material to draw from/ draw on. Or you want to sing/write about God's majesty and glory? The books of Isaiah and Revelations provide material for that. Or you want to sing or write about Jesus' love and nature and miracles? The books of Matthew, Mark, Luke and John provide that.