I helped my dad put up stem wall forms for the work shop he was building in his back yard. I thought it was great that he planned to do it himself, with only minimal help from a few relatives.
Though I knew nothing about the process, all I had to do was follow his instructions. We put up big sheets of plywood vertically, and we propped them up with 2x4's placed at an angle to the ground.
When we had the forms complete with the empty space in the middle, we had my uncle come in and pour the concrete into the gap. The result was a perfectly solid concrete stem wall that could stand on its own.