Hebrews 11:1 (New King James) Now faith is the substance of things hoped for, the evidence of things not seen.
Hebrews 11:1 (New Living Translation) Faith is the confidence that what we hope for will actually happen; it gives us assurance about things we can not see.
When we read Hebrews chapter 11 we see tremendous examples of faithful people. Such examples mentioned are the faith of Noah. A man who built a large boat to save his family from a flood. A flood of which had never happened before. God had warned him about this flood so Noah went to work and obeyed God in building the Ark. Because of his faith his family was saved and the rest of the world condemned.
Look at Sarah. She was much to old to have children yet even though she was old and barren, she believed in God's promise that she would have a child. Eventually a whole nation came from this one child as promised by God. Hebrews 11:18, "Isaac is the son through whom your descendants will be counted." Sarah believed in God's promises. She may not have understood how she could have a child, but she believed she would because God said she would. God keeps his promises.
Look at Abraham. He showed tremendous faith when God told him to sacrifice his only son Isaac. Even though God had told him that Isaac would be the man whom your descendants would be counted, Abraham knew that God keeps his promises so he raised his knife to sacrifice his son. He may not have understood how God could keep his promise but he believed that if he obeyed God and sacrificed his son that God could bring him back from the dead and bring him back to life again to fulfil his promise. So by faith he proceeded to sacrifice Isaac. We know that God stopped Isaac from being sacrificed as an angel stopped Abraham at the last second. God provided a Ram stuck in the thicket to offer as a sacrifice instead.
Faith is the confidence that what we hope for will actually happen. Faith gives us assurance about things to come. Just the three examples I mentioned show us how true this is. I think it's important to know that to have faith you must believe that God is who he says he is and he does what he says he will. Knowing God's character is the beginning of faith. This is what gives us the confidence that what we hope for will happen. The ending of faith is God doing what he says he will. It's God's promises being fulfilled. This is what gives us the assurance about things to come. To have faith is to believe that God is who he says he is and because of this we can trust with certainty that the things we hope for will come to pass. God always keeps his promises. Even though we may not understand or see how our faith can possibly work out. We can trust in God's character and his promises, and that's all we need.