To prevent the clay from sticking to the molds, use some sort of release agent. For this project, we prefer to mist the molds with a little bit of water from a spray bottle, but you can also use cornstarch, baby powder, or whatever release agent you like.
Put a piece of black clay between the two molds and press them together. The amount of clay depends on the size of the coin; for this coin, we used a ball about 3/4” big. Line up the marks you made in the previous step to match the pattern on both sides of the coin.