In the Book of Matthew in the Bible, it says "Ask and ye shall receive. Seek and ye shall find. Knock and it shall be opened unto you." When you go up to a house and the door is closed, what can you do? You can ask other people if someone lives there, who they are, what they are like. But how can you know for sure? How do you know they aren't making it up? How do you know someone really is there? You go up to the house and knock.
The same can be said about God. You can ask others if He exists and what He is like. But how can you know for sure without "knocking?"
Pray. Praying is knocking upon Heaven's door and waiting for God to answer. You'll get your answer.
Along with evidence of His marvelous creations all around you, Heavenly Father has given you many ways to know for yourself that He lives. You can: