Turn the garment inside out.
Then look at teh other seems. You can basically pin the item together in the proper way to hold the fabric together while you sew. Then neatly whip stich the area. A whip stitch is basically a spiral. Like if it is the seem of a pants leg, you have them inside out, then you stitch through the seem, come back over the top and back through again just net to where you started. If the pants were invisible and you could see the thread, you could tell it woudl look like a long thin spiral along the length of the seem. got it?