Great question and one that is not that uncommon of many Christians. Praying out loud isn’t easy and not everyone is comfortable in praying amongst a group of people. I would recommend to start praying out loud alone, in your bedroom or at the dinner table. Then, try and pray with a small group of friends. Maybe each one of you saying a sentence or two, thanking God for His goodness. If you can remind yourself that you are talking to God like you would a friend, that can allow you to be more comfortable.