Faith is one of those "outside the rectangle" things.
It's about what you can't see but you know is real, because eg. you've
grown up with it and saw in your family or Synagogue or church that God was there,
or seen God answer prayer,
heard about miracles,
read in the Bible and knew that it was true,
had angelic visitations or God dreams
or knew in your heart that Jesus could save you.
A lot of people don't have faith because they only dare to believe in the ordinary - the things that can be seen or proven academically.
That feels nice and safe, but it's a deception. Trying to believe by first working it out is going about it the wrong way round.
I've seen a lot of people trying this approach and they got nowhere.
I wrote a parable about this in my stories section.
The Bible says faith starts with something that happens in your heart.
It tells us to love God with all your heart, soul and strength (Deut 6:5) and that if we believe in our hearts we will be saved (Rom 10:9).
There are many things you can't see, such as eg nuclear radiation, that can be downright dangerous if you don't believe in them.
On the other hand blind faith (ie believing anything) can be just as bad.
Faith in God is something that will prove itself in the long haul, because God is faithful.