We cut panties according to the division We cut the gusset along the grain. 
Finished gusset is approximately 13 cm

1. Sew on the central elastic band on the butt
2. Process the gusset
3. Sew on the gusset

4. We process the cutout lines for the legs with an elastic band.
Method 1 - we lay 2 seams with a straight stitch - one closer to the left edge, the second - along the right edge, then cut off the excess, tuck and stitch with a zigzag
Method 2 - we lay 1 seam with a straight stitch in the center, then turn it under, sew with a zigzag and cut off the excess

5. We process the upper seams with an elastic band (in any of 2 ways)
6. We create a “tick” (the cut of the central elastic band at the back should be hidden under this “tick”)