U may ask Ur'self >"How can I learn to truly believe in God?"

When you surrender all to God and put all of your trust in him, you will see him working in your life and you will just know. Bible study, fellowship, church, and testimonies are all helpful for witnessing God's work.
And also Read the Bible, especially the New Testament. Find a local church and attend their sermons or Bible studies. You can also study Christian apologetics to learn how to defend the Bible.