Chives and onions grow like weeds from seed. Just start them as you would any other seeds, in a flat with seedstarting mix. I usually grow my onions by putting a mesh flat full of seedstarting mix into a no holes flat, moisten it well, sow the seeds on the surface and cover it with a clear germination dome and keep it warm until they are up about an inch tall, then move them to the greenhouse in full light.
When the roots have the soil bound together, then you can remove the mesh flat out of the no holes flat. If the tops get real tall and start falling over, trim them off to a couple of inches with scissors.
Pull them apart to transplant. As long as they are as big as a piece of spaghetti when you transplant they will grow great big onions.
Chives are exactly the same as onions in seed care.