Faith is the noun form of the word, to believe.
Faith is the substance of things hoped for, the evidence of things not seen, Hebrews 11:1.
Faith is the confidence, the belief, the trust in someone or something that is supported by claims and evidence (regardless of the veracity of those claims and evidence) that a person or thing can do or be what the claims and evidence demonstrate to us. Having faith in an object doesn't create the object's capability. If valid, the object is worth trusting, based on the claims and evidence made by/of the object.
Faith is not a verb or noun that specifically pertains to spiritual things, or things of a spiritual nature, like one can have faith that a chair will support one's weight, or that a car will enable you to get from point A to point B without failing.
Faith is exercised at many points along one's life. In the Christian context, faith is exercised in the Lord Jesus, based on His claims and the evidence of Who he is, before we come to Christ as our Lord and Saviour, at which point, we are born of the Spirit of God.
We also exercise faith on a daily basis as we continue in the journey of faith in our relationship with the Lord Jesus Christ, and our His work in us through the Holy Spirit.