You can know for yourself that these things are true by asking Heavenly Father in prayer. He will answer you through the Holy Ghost. The Holy Ghost is also called the Spirit of God, and one of His roles is to witness, or testify, of the truth. The Holy Ghost reveals and confirms truth through feelings, thoughts, and impressions. The feelings that come from the Holy Ghost are powerful, but they are also usually gentle and quiet. As taught in the Bible, “The fruit of the Spirit is love, joy, peace, longsuffering, gentleness, goodness, faith, meekness, [and] temperance” (Galatians 5:22–23). These feelings are a confirmation from the Holy Ghost that this message is true. You will then need to choose whether you will live in harmony with the teachings of Jesus Christ as restored through Joseph Smith.