I learned to make a flat-fell seam when I sewed pajamas for my siblings many years ago.  This is an easy way to sew a seam that conceals all raw edges - it is common in many shirts.  The seam has 3 main steps:  1) Place the fabrics wrong sides together and sew a 5/8" seam allowance.  2)  Trim only one of the seam allowances to about 1/4" - 3/8".  3) Press the remaining seam allowance over the trimmed, turn the raw edge under, and stitch on the fold to finish the seam.