Mark the buttonhole length on the fabric
Reinforce the area with interfacing if needed
Set the sewing machine to the buttonhole stitch
Place the fabric under the presser foot
Sew the first side of the buttonhole
Sew the bar tack at one end
Sew the second side of the buttonhole
Sew the second bar tack at the other end
Remove the fabric from the machine
Cut the center of the buttonhole open carefully
Use a seam ripper or small scissors
Stop cutting before reaching the bar tacks
Secure loose threads if needed