Since its founding, this nation has been deeply influenced by the Bible and the Christian faith, and many people in our nation have a strong commitment to Christ and are seeking to follow Him in their daily lives.
But only a minority of our citizens are active Christians, and America is not a fully "Christian" nation. Nor does Christianity have a special legal status in our country. People are free under our Constitution to practice all kinds of religious beliefs, or to practice no religion at all. In fact, in recent years, we've seen an upsurge in secularism (which is the idea that life should be lived without any regard for God).
Regrettably, you are right when you say that God doesn't seem to make a difference to most people. But He should, for He is the Creator of the universe, and we are accountable to Him for the way we live. The Bible (which tells us who God is and how He wants us to live) warns that "Man is destined to die once, and after that to face judgment" (Hebrews 9:27).
During your time here I hope you will become acquainted with some men and women who take Jesus seriously and try to live the way He wants them to. In addition, I urge you to get a Bible and begin reading about Jesus in one of the Gospels. When you do, you will discover that God loves you, and you can come to know Him personally by giving your life to Jesus Christ.