Faith, pistos, is conviction of the truth of anything, trust or confidence springing from that conviction. The original Greek term is "...used especially of the faith by which a man embraces Jesus, i.e., a conviction, full of joyful trust, that Jesus is the Messiah -- the divinely appointed author of eternal salvation in the kingdom of God, conjoined with obedience to Christ." (Thayer's Greek-English Lexicon, p. 511)
The Biblical definition of faith is found in Hebrews 11:1: "Now faith is the substance of things hoped for, the evidence of things not seen." Since hope is desire with expectation (see Romans 8:24-25), there must be some basis or reason to expect a desire to be realized. This basis is faith. Faith is the "substance," hupostasis, i.e., the "thing put under, substructure, foundation." (Thayer, 645) Since the things hoped for are not seen, yet the proof or evidence, elenchos, that they exist is faith.
We are convinced of the reality of things unseen by the truth or confidence we have in God. If someone we love, respect and trust promises us something -- a gift, trip, etc., though we have not seen the promised thing we desire and expect it. Why? Because of the confidence we have in the integrity and honesty of the person who promised it.
What evidence is there that there is a Paris or London, or that George Washington or Abraham Lincoln really lived? Have you seen these places or men? The fact that they are, or were, is accepted by faith. You trust those who informed you.
There is a heaven, etc., and as faithful Christians we expect to go there. The evidence? The basis for hope? God, who cannot lie (Heb. 6:18), has told us. We believe Him.
"But without faith it is impossible to please Him, for he who comes to God must believe that He is, and that He is a rewarder of those who diligently seek Him" (Heb. 11:6).
Since it is by faith that one obeys God in entering into an approved relationship with Him (Gal. 5:6) and lives a life approved by Him (Gal. 3:11), it follows that faith is necessary to please God (Heb. 11:6; John 8:24). Faith must be in one's heart in becoming a Christian and it must be retained and even augmented throughout his life as a Christian (Rom. 5:1; 2 Cor. 5:7). There is no sin more devastating than the sin of unbelief because it eliminates every phase of usefulness before the Lord (John 3:18). Unbelief, which so easily besets a person (Heb. 12:1), keeps him from fellowship with the living God (Heb. 3:12).
Trust and confidence comes through a knowledge of God -- His character, love, dependability, sovereignty, etc. -- revealed in Scripture, thus faith comes by hearing the word of God (Rom. 10:17).
Since faith only comes by hearing the word of God, go to the Scriptures, His inspired word, to learn of Him and Jesus Christ, His only begotten Son who lived and died for you. Allow the facts presented in the Bible about them to generate faith in your heart and then manifest that faith by submitting in obedience to the gospel, God's power unto salvation (Rom. 1:16), so that you might have your sins remitted (Acts 2:38); be added to Christ's church, the body of the saved (Acts 2:47); and have the hope of eternal life (1 Pet. 1:4).