Most definately color your fondant first like maybe a "Wilton Dandilion" yellow first. That's what I use. Or any dark shade of yellow will work fine. Roll out the fondant into a log (not too thick) make sure it's a little bit longer than the mold. Dry dust the inside of the mold, not too light because then it won't show up very well on the final pearl strand. With the mold open wide, press it down onto the log of fondant, push it down and squeeze it closed. Flip the mold over and trim off the excess on the ends and I usually take one of my tiny Pampered Chef paring/utility knives and slide it along the top of the mold to trim off any excess fondant that squeezed out. Very carefully squeeze the mold open with one hand and with the other hand either with a toothpick or a paring knife start at the furthest end of the mold from you carefully pick out the strand until it falls out on it's own. Let gravity try to do most of the work on getting it out of there or else you risk denting the individual pearls if you have to force it out too much. If your fondant sticks which has been known to happen with MMF, I very lightly spray my mold with a non-stick spray and dab off excess spray. (Use that tip only if your fondant sticks)
Let the pearl strand dry a few minutes before placing on the cake if you are placing strands or if you are going to trim them off and use them individually.
This is how I make my pearls! So this is what works for me! Hopefully it will work for you. Try some practice strands now so you get comfortable using it!
Hope this helps.