I rooted mine in rock wool so I just put that in the hydroton once it was rooted. I've seen other people that didn't use rock wool and they just carefully held the plant in the net pot at the proper height and gently added the hydroton until it was nicely supported. i added about an inch or so of hydroton in the bottom of the net pot then made the roots rest on that then fill in around. you will get plenty of water splashing up on your hydroton to excite the roots in the beginning so they don't need to be totally submerged. I like to keep my water just barely touching the bottom of my net pots...doesn't suffocate the plant and serves as a good reference point to see how much water she is drinking as she matures.
I've been learning a lot as I go and have trial and error tested quite a few things...I think the most important thing I've learned with DWC is that you will use fewer nutrients than other methods and that you have to invest more time monitoring your environment. I printed off a blank calender from google images and I write down PH, PPM , temp, humidity and anything I add to the reservoir on a daily basis before my lights kick off (missed a few days of course). It really lets me see how much the plant is taking in.
Also, it REALLY helps to have the proper beneficial microbes and enzymes in your res. read the section on here under dwc on how to make microbe "tea", or buy pre-made products to acomplish this (what I did) This will prevent root slime and decay problems that are very hard to avoid without taking measures....
I could go on and on but if you have any more questions as you go, don't hesitate to post on here and someone will surely help... Peace