Put the first block at the desired height and correct level. Using this first edging block as your guide, lay the rest of the blocks keeping them straight and uniform. The tops of the blocks should sit just a bit above the ground. Depending on the shape and size of your garden, you might need to cut some of the bricks or stones to make them fit. You can rent a brick saw to make any needed cuts. An angle grinder with a stone cutting blade can also do the job.
When edging with brick or stone blocks, be aware of the height of your edging. They might not be safe to go over with a mower.
Nice work! Not only will your new edging make your garden look like it was installed by a professional, the edging will last for many years.