Prayer is an essential part in coming to know our Father in Heaven. It's how we communicate with Him. Through the Holy Ghost we can receive promptings and thoughts that help us to know what our Heavenly Father wants us to do. As missionaries for the Church of Jesus Christ of Latter-day Saints we invite people to read the Book of Mormon and to ask God if it is true. We cannot convince anyone of this by ourselves. The Spirit is what truly converts each of us.
An example of this would be... me. My parents taught me about Jesus Christ and about the Book of Mormon. As a child I may have taken their word for it. But as I grew older I realized that I needed to know for myself. I read and studied the Book of Mormon and then prayed to God asking Him if it was true. I can testify that it is. I didn't have an angel appear to me and proclaim its truthfulness, I didn't see a vision, but I did feel something deep in my heart confirming to me that what I had been taught was true. Everybody can receive an answer for themselves. You just have to ask.