The beauty of the single row buttonhole is that the whole thing fits within a single row. This is a great technique to learn because it's strong and doesn't take much planning. I use it a lot when I'm improvising sweaters for dolls or little kids.
The technique has a lot of steps and can seem a little complicated to new knitters. I know I prefer a video when I'm learning a new knit stitch or technique so I made one to help you through the single row buttonhole.
With right side facing, move yarn to front, slip a stitch, move yarn to back and leave it there. *Slip another stitch, pass first slipped stitch over second. * Repeat part between * two more times for a total of 3 cast off stitches. Slip last slipped stitch back onto left needle. Turn work. Move yarn to back and use the cable cast-on to cast on 4 stitches on the left needle. Slip first stitch from right needle to left needle and pass last cast on stitch over it. Slip first stitch on left needle back to right needle. Turn work, move yarn to back, continue to work the row.
You can cast off more or less stitches depending on the size of your button. Always cast on one more stitch for the top of the buttonhole than you cast off for the bottom.