God is invisible...but that doesn't mean he's not real.
And that's the problem: since we are prone to only believe what we can see, we simply don't believe God is real.
What about "gravity?" Do you believe in gravity? How about "air?"
You can't see or touch gravity or air, yet they are both real.
You say you believe in God? You do well, but even devils believe in God, and tremble. (James 2:19)
You see, it's not about believing IN God...it's about BELIEVING God.
Not everyone is a child of God. Only those whom God has chosen can "see" him. He will reveal himself to them in his time, in his way, according to his purpose. You must just ask him to reveal himself.
If you want to "see" the invisible and know, without a doubt, that God is real, pray as I prayed over thirty years ago, "God, if you're real, I want to know."
Until you know, without a doubt, that God is real...nothing else really matters.