There are many ways to seam knitted pieces together. Many of those ways are meant to be used only in certain cases. .
Backstitch is perfect for beginners as you get quick results, and it’s very hard to get muddled with one straight line of sewing. I think back stitch is one of the best embroidery stitches, giving quick and neat results without too much fuss
In the video tutorial, we have used a different yarn in a contrasting color, but typically you would use the same yarn as your knit pieces.