I guess first off you need to know that faith is not something you have so much as it is something you DO! The analogy I like to use to describe doing faith is comparing it to hope. If I hope the sun will rise tomorrow then I wont do anything to plan for it. I will just sit and 'hope' it comes. I won't make plans because it might not. If it comes I will deal with it then. If I have faith tomorrow will come I will plan for tomorrow. I will actively pursue tomorrows events today, because I have faith it will come. Instead of just sitting and hoping I'm exercising my faith in tomorrow coming by making tomorrow happen before it gets here. To relate that to Faith in Christ, if we hope that Christ atoned for our sins we would sit and wait till we died to find out. We would want to hope Christ was there for us but we wouldn't turn to him cause we would be unsure. When we have faith in Christ we use his atonement by asking for his forgiveness, we may not have a 'perfect knowledge' that he atoned for our sins but because we have faith in him we exercise it by actively applying the atonement into our lives. By doing this small act of faith we are following the council given in Alma 32.
33 And now, behold, because ye have tried the experiment, and planted the seed, and it swelleth and sprouteth, and beginneth to grow, ye must needs know that the seed is good.
34 And now, behold, is your aknowledge bperfect? Yea, your knowledge is perfect in that thing, and your cfaith is dormant; and this because you know, for ye know that the word hath swelled your souls, and ye also know that it hath sprouted up, that your understanding doth begin to be enlightened, and your dmind doth begin to expand.
35 O then, is not this real? I say unto you, Yea, because it is alight; and whatsoever is light, is bgood, because it is discernible, therefore ye must know that it is good; and now behold, after ye have tasted this light is your knowledge perfect?
36 Behold I say unto you, Nay; neither must ye lay aside your faith, for ye have only exercised your faith to plant the seed that ye might try the experiment to know if the seed was good.
When we have tried the experiment and planted the seed we are using our faith as a verb. We are trusting in out Heavenly Father and Jesus Christ and as the seed grows into a plant and tree so will our faith grow larger and stronger as we continue to act upon it.