What is a seam?
A seam is the "line" where two or more layers of fabric are held together with stitches. Sew cute pattern always have a plain seam. This is the most common type of machine-sewn seam. It joins two pieces of fabric together face-to-face by sewing through both pieces, leaving a seam allowance.
Some patterns will have a seam allowance built into the pattern page, some won't. If the pattern tells you to cut the pattern leaving a 1/4" seam, you will cut leaving about 1/4" of fabric after the pattern ends.