Personally I start my
seeds by placing them on a wet/damp paper towel that I placed inside a small Tupperware container with a lid. The lid is important to keep humidity in. Then once they sprout I place them in the rockwool cubes. I used to just start them in the rockwool cubes, but I was needing to through away all the cubes for those seeds that did not sprout. Mainly because of mold/fungus that would grow on them because of all the water,
nutrients and light. I don't want to transfer any diseases to any new seeds if I tried to use them again, and it's more work than I'm willing to do to try to sanitize them with bleach water or H2O2.
I have no trouble sprouting them in the Tupperware containers (except for spinach that I now understand sprouts at low temperatures), and moving the sprouts to the rockwool with my fingers, a butter knife, or tweezers depending on the size of the seeds. So now I just make sure they sprout before I put them in the rockwool cubes so I don't wind up wasting them.