Questions...
If I believe in God, what should I do next?
We must understand that sin is when we disobey God, so God is looking for us to begin the process of changing that. How? We do that by making a conscious decision toward changing the direction of our lives, and begin our steps in obeying God. There is word for this, it is called repentance. God is looking, looking, looking for people with at least that spark of a desire--because that's the essence of workable material for Him.
The Lord is not slack concerning his promise, as some men count slackness; but is longsuffering to us-ward, not willing that any should perish, but that all should come to repentance. (2 Peter 3:9)