what to do next?

ok so this is my first grow ever...white widow..i have a hydroponics setup already and right now my seeds are in moist paper towels...when the root comes out what do i do next? do i put them in the rockwool and put it in my hydro setup? or do i just put them in the rockwool cubes and keep the cubes most until i see the first 2 leaves then plant them in the hydro set up? i searched already and im kinda confused...do i use light food etc yet??tanks