Here's how Hebrews 11:1 puts it: Weymouth New Testament
Now faith is a well-grounded assurance of that for which we hope, and a conviction of the reality of things which we do not see.
So, I look at it like this; if I have seen someone's work many times in the past, or have come to trust a person to live up to their word, my faith in them grows when it comes to believing that they will do something in the future. It is based on their track record.
So,even though I haven't 'seen' that of which they speak, I have faith they will fulfill that of which they speak.
It is like a guarantee of sorts. To simplify it, imagine you ordered something from Amazon. You would get a confirmation that you would receive your order. You would then have faith that you would receive, even though you obviously do not have the item in your hands yet. Based on the fact that Amazon have a track record of being faithful to their word you would have faith in them. Ie, they will deliver as promised.
And so, with faith in God, based on his track record in the Bible, on say, his protection of his people, I have faith that he will protect his people today when he says he will.
Isaiah 41:10
'Do not fear, for I am with you; Do not anxiously look about you, for I am your God. I will strengthen you, surely I will help you, Surely I will uphold you with My righteous right hand.'