I start my seed in papertowels. When they crack they go into RW in the res with water only until they have 4 true leaves or two nodes (little round ones the seed uses to break out of the shell don't count they die a week or two into the grow). Some start the seeds right in the rock wool with good success.
Both will work but if you are new to hydro, do the papertowel method. I soak my seeds in a cup of 5.5 ph water only until the seeds sink to the bottom of the cup. They will float for anywhere from a couple of hours to about 1/2 day ( I do it overnight). I remove them within a couple of hours after they sink, use the water only to wet the papertowel placed on a styro plate, put the soaked seeds on the wet papertowel and fold it into 4ths. I then cover with a bowl and put the plate on my computer router for some gentile underheat and within a day or two I have cracked seeds with 1/4" tails that I insert in a working BP system. I put a new hole in the rockwool ( the preexisting holed is too deep and better used for clones - turn the cube over to the no hole side and make your own - I use a tweezers). When I plant a cracked seed I insert it only deep enough to cover the top of the seed. You'll see a fine shoot within days and it's off to the races from there.
Lots of ways will work but so far I have 100% success rate with this method. Had three bagseed grows and two with Barney's Farm LSD. This time I'm doing LSD, Sannie's Jack and Subcool's Pandora's box all from seed.