This stitch follows the same technique as a simple chain stitch. The only difference between the two is that a double chain stitch is done over two parallel stitch lines, instead of one. Thus, in the end, the visual effect is that it looks more or less like an open feather stitch.
To be able to do this stitch, it is good if you are aware of the chain stitch technique. I will be working on two straight parallel stitch lines, from bottom to top. All the stitch points will lie on the stitch line.