Perhaps one of the most basic principles of any religion is the concept of faith. Faith as denoted from the scriptures, "is not to have a perfect knowledge of things; therefore if ye have faith ye hope for things which are not seen, which are true." (Alma 32:21) Every single person exercises faith in some way each day.
It can be in as simple as flipping a light switch on. You cannot see the wires in the walls that are connecting that light bulb to electricity but you exercise faith when you take the action to flip the switch. After you have done it enough times it becomes an expectation that when you flip the switch, it will turn the light on.
Faith in Jesus Christ is the same way. Having faith in Christ includes having a firm belief that He is the Only Begotten Son of God and the Savior and Redeemer of the world. As we accept and apply his atonement (His suffering, death, and resurrection unto the saving of our souls) along with his teachings- we are exercising faith. It will bring a light into our life far beyond that of a light bulb. The light that Jesus Christ offers us is the hope that we can receive Eternal Life and once again live with our Father in Heaven.
Examples of Faith seen throughout the scriptures. A list of many instances where faith has been exerted by ancient prophets and followers can be found in Hebrews 11. True faith brings the lasting peace and assurance that through Jesus Christ we can receive a remission of our sins and one day return to our loving Father in heaven.
God blesses those who have faith to obey His Son. In fact, God blesses any and all of his children who follow his commandments, pursue a Christ-like life, and/or partake in the ordinances of salvation. God promises Eternal life to all who follow his commandments and remain faithful their entire lives. See (D&C 14:7)
True faith in Christ leads to action. It leads to sincere and lasting repentance.