faith is the substance of things hoped for...? What does it mean?

faith is the substance of things hoped for,
the evidence of things not seen.
Hebrews 11:1

I don't understand. There are many many things that I haven't been able to understand what they mean in the bible. However it is a true joy when I came to understand the hidden meaning. It felt like I found the treasure. The parables of the widow who offered two coins and workers of the vineyard who get paid the same amount taught me the love of God and made me realize how selfish and arrogant I was. I still don't understand the story of prodigal son as I sympathizes the other though.

Last week during the service, sang a hymn called "Are you able" which goes like

Are ye a-ble, to re-mem-ber,
When a thief lifts up his eyes,
That his par-doned soul is wor-thy
Of a place in Par-a-dise?

Then suddenly I felt sorry and ashamed.
People say so easily to kill someone, not worth living, waste of social benefit. They are better than the other and think they can control the others life. I am not different at some point.
However are we? We are born with nothing, just the same human-being and God's children.
Even Jesus pardoned the thief, how can I judge someone?
People claim to be righteous for their faith not the behavior as it is written There is none righteous, no, not one...that a man is justified by faith apart from the deeds of the law. (Rome Chap.3)

Then here comes my question. What is faith?
As faith is the substance of things hoped for,
the evidence of things not seen.

What should I hope for? What is the substance?
If i cannot see, who can it be the evidence?