The most important thing I can tell you is that God doesn't want you to have a shaky, insecure faith. He wants you to know beyond all doubt that He exists -- and not only that He exists, but that you can know Him and have a personal relationship with Him.
How is this possible? It's possible because God did something that staggers our imagination: He became a man. That man was Jesus Christ, and one reason He left heaven and came into the world was so we could know what God is like. He proved He was God by doing something no one else had ever done, or ever will do: He conquered death's power and came back from the grave.
Do you want to know what God is like? Look at Jesus Christ as He is found in the Gospels of the New Testament. And when you do, you'll discover not only that God exists, but that He loves you and has opened the way for you to be with Him in heaven forever. The Bible says, "No one has ever seen God, but the one and only Son, who is himself God and is in closest relationship with the Father, has made him known" (John 1:18).
By a simple prayer of faith confess your doubts and your sins to God, and then ask Jesus Christ to come into your life -- and He will. The Bible says, "For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life" (John 3:16).