Fold the top fabric and create a crease along the folded edge. Thread a curved needle with your choice of thread and tie a knot in the end.

Secure with two holding stitches in the base fabric hidden under the edge of the top fabric.

When creating the second holding stitch, ensure to bring the needle out of the base fabric in line with the creased folded edge of the top fabric.

Draw the thread through to the surface

Lay the thread onto the top fabric at 90º to the crease and take the needle into the crease just behind the laid thread.

Bring the needle out further along the crease.

Draw the thread through, lay the thread on the base fabric at 90º to the folded crease, take the curved needle through the base fabric just behind the laid thread and out a little further along in line with the creased edge.
Aim to achieve an equal stitch length to the previous stitch

Repeat the last few steps to stitch the two fabrics together.

Every two to four stitches pull on the thread with increased tension to straighten the path of the thread and close the gap between the two threads, this should hide the thread to achieve invisible stitches.
Don’t forget to cut off the waste knot from the holding stitches.