Here’s my seeders.
They are different for numbers of seeds that I can put into: little seed into little “pot”.
They are about 40×60 cm and high 3 cm, at the bottom of the “pot” there is a hole from where water is in contact with soil. I put the seeder into a bin with water so to have soil always wet, and put all into warm place (no less of 18C degree), with high level of illumination.
The PVC one is for seeds like pepper, beans, peas, cucumbers or tomatoes.
The three others are for onions, celery, salads, cucurbitacae, fennels, borrago, basil, melon, chard and radish.
Usually carrots, spinaches, garlic, onions, shallot, potatoes and sweet potatoes are put directly into soil out there, when dangers of frost are away.
If you create a backyeard on balcony, you can use for seeding your final pots.