Laminate floors are usually made of particle board or some other type of manufactured wood composite overlaid with either laminated wood veneer or, more typically, plastic or paper that's designed to look like wood. Laminate floors are fairly durable, but dropping a heavy object on one is going to dent the surface. Since a laminate floor is not a wood surface, you can't treat it as such when making repairs, but it is possible to repair dents in your laminate floor with wax putty and a few other simple supplies.
Buff the dented area with the sandpaper, pressing the sandpaper paper into the dent with your fingertips. Use quick, light strokes to remove the shine from the surface inside the dent; you want a dull surface so the putty will stick to it. Blow away the dust.
Scoop up enough putty to fill the dent, plus some extra, with your plastic putty knife. Wipe the putty into the dent, then run the flat end of the knife over the top of the hole to flatten it out and make it even with the surface. Make sure to take up any excess putty off the surrounding surface of the floor.
Let the putty set according to the instructions on the packaging (generally, an hour or two). Gently buff the whole area with a clean cotton cloth.
If you're dealing with a scratch that's too small to use putty, use a standard brown wax crayon of the closest shade to the floor that you can find, gently running the tip of the crayon along the scratch until it's gone. Avoid sanding any area of the floor outside the dent.