Its not really unless you make it such.
Just a bucket or container filled with aged water, throw in a few leaves and or grass clippings, float some small bits of drift wood or similar ( drift wood adds tannins which the mossies like)
Leave if for a week or so then keep an eye out for egg rafts.
image borrowed from mother google
These will then slowly get smaller as the eggs hatch and you should begin to see the larvae wriggling. Depending on the size you need as to how long you leave them before harvesting. As mentioned above, I sometime take the eggs inside in a jar of the water and hatch them inside, The newly hatched larvae are great for fry.