I think he is referring to placing a small wooden frame in the ground, one with a lid, that stretches the growing season in the spring and fall. The hinged lid will have plastic sheeting stapled to it and can be opened during the day and closed at night. Bigger boxes can be used for hardening plants before transplanting.
It gives a little more growing time outdoors at both ends of the growing season in northern areas where the danger of frost is present for tender plants.
Most boxes aren't all that big, and can be compared to a miniature hothouse, big enough for a couple of plants. I have heard of some sensitive plants being planted way early, especially Lettuce, in such boxes.
I toyed with them many moons ago, right after I first got married and we lived in an Apartment, with little growing space or opportunity.
If that is not what he is referring to, then I don't know and can't help him. He could also mean Window Boxes or Patio Containers, which if you are hard for space, is not a bad idea.
I grow Grape Tomato's in a container, only because they do very well there, and are easy to maintain.
