[header] How to gusset pants [title] Open up the seam of your pants (optional). [step] If you are adding a gusset to finished pants, then you will need to open up the seam to make room for the gusset. Use a seam ripper to open up the seams around the crotch area. 
Seam rippers look like a two pronged fork with two different sized prongs. Use the long point of the seam ripper to catch stitches and the blade in the center of the two prongs will cut the seam.