All seeds are started in flats, so that you can choose the strongest seedlings to transplant and so that the crops that are already growing in the beds have a few more weeks to mature before the new seedlings are put in. These are half flats, which are easier to carry that the full flats.
The little tool in Ed's right hand is called a widger: you use it to lever the seedling out of the first flat...
...and then you use it again in the new flat to open up a space in the soil for the seedling. It's not difficult but it does take some practice.
A full flat. These can weigh quite a bit when they're full of wet dirt!