To make it a bit easier to understand here is a step by step construction method for you.
Before we start a few guides
Right side – the face, front or outside of the fabric
Wrong side – the interior, inside, back of the fabric
Step 1 – Front, back and gusset all right side up.
Step 2 – Gusset right side up.
Step 3 – Gusset right side up with front edge finished. I’ve overlocked it, you could overlock/serge the edge or zig zag.
Step 4 – Front panel, right side up.
Front panel with back panel placed on top. The right sides have been matched together so the photo shows the wrong side of the back panel facing up.
From the photo above, we have now added the gusset with the right side matched to the wrong side of the back panel. Photograph shows the wrong side facing up of the gusset.
Step 5 – pin at crotch seam.
Step 6 – 1cm seam allowance, straight stitch seam.
Step 7 – finish raw edge of seam, again I have overlocked but you could overlock/serge the edge or zig zag.
Step 8 – place seam flat and press. Photo now shows the wrong side of both front and back panels but the right side up of the gusset.
From here you can follow along with the rest of the instructions to complete your knickers.
I hope this makes it clearer and if you have any questions, please let me know.
Enjoy making your knickers!