Prayer is simply our sincere talking to God. We don't pray to God to impress others. We pray to God to communicate with God, what is on out heart, our needs and our wants.
Does God already know what is going on? Yes, of course. But in a relationship with someone we share with them about what our heart is struggling with. The same is with God. It starts out when we are baby Christian, as a one way conversation. As we grow we come to realize how God communicates to us and our prayer becomes part of our ongoing relationship with God.