Just how there is no "proof" for the existence of "dark energy", there is no "proof" that there is a God but there can be individual conviction and knowledge given that they have a Heavenly Father that loves and cares for them who pours blessings from heaven onto heads of the righteous as they obey higher laws not of this world. It all starts with faith.
Faith is a tricky thing however because it has to be based on principles of truth. Some lose this faith in God because of pride, politics, and finite learning. For me I know that there is a God and that he loves me. He created me and is encouraging me to follow paths that will lead to my happiness. I pray to him. That might sound weird to some, that I would kneel down and talk to a being that is far away in hopes to petition him for some extra help beyond my own abilities. For me however it is just like going over to my parent's house and having a conversation with my Dad in the garage.