Whether you grow in rockwool, perlite, or another medium, it is easiest to start the seeds in rockwool cubes.
You can buy plastic trays with pre-cut rockwool cubes, or you can purchase a big slab of rockwool and cut off small cubes of 1 inch thick and 2 inches tal. Put them in small cups. Make sure that each cup has a hole for drainage, otherwise the roots will rot.
Make a hole in the top of each rockwool cube, wide enough to drop a seed in, about half an inch deep. Water the cubes thoroughly, letting excess water run off.
Drop the seeds in the holes, one seed per hole.
Put the cubes under fluorescents lights. It doesn't have to be strong light, 40 Watts will do. Hang the lights 2-3 inches above the cubes. This will provide maximum exposure to the light, and the warmth generated by the lights will facilitate sprouting. Keep the lights on all day and night.
Make sure that the room temperature is about 25 C or 90 F. If necessary, buy a heating mat from a gardening store and put it under the cups or tray.
After several days, the seeds will sprout.
When the seeds sprout, check daily that the lights are high enough over the seedlings. If necessary, raise the lights to give the seedlings room. At this stage, they grow very fast.
About 3-5 days after the seeds sprout, the roots will show through the bottom of the rockwool cube. This is the right time to transplant the seedlings. Prepare a bigger slab of rockwool by cutting out a space for the cube and water the rockwool thoroughly. Use tepid water so that the seedling won't get a shock. Carefully take the rockwool cube out of its paper cup or other holder, making sure that you don't touch the roots that poke through the cube and that the roots don't get damaged in any other way, such as rubbing the cube against the cup. Place the cube into the hole that you cut out in the big rockwool slab. If at this stage you discover that the hole is not big enough, don't try to press the cube into the hole. Instead, gently remove the cube and make the hole bigger.
Make sure that the small cube does not sink in the hole lower than the rest of the surface. The small cube should rather stick out a bit. This prevents stem rot, which otherwise might occur if water can form a puddle at the base of the stem.
After the transplanting you can start adding nutrients to the water. There are special mixes for seedlings and transplanted plants. If you use nutrients that are not specifically for seedlings, use half the dosage.