Satin stitch is a good way of sealing the edges of a project or filling in a space in embroidery, for example a leaf or a flower. It is basically a zig zag stitch but with the stitches right next to each other rather than spaced out.
It is possible to mark out the area for satin stitching with a fabric marker pen, but I think it gives a much neater finish if you edge the area with a small running stitch.
Beginning from one side of the shape to be satin stitched, push the needle into the fabric at the bottom of the shape and bring it out at the top. Then push it in at the bottom again very slightly to the left of the first stitch and bring it out at the top slightly to the left.
Continue working across the fabric with stitches close together. Use your thumb to flatten the satin stitches so that the shape lies flat.
The gift label on the left was satin stitched by machine. Just set your machine to wide zigzag with very small stitch length. The springbok on the right was satin stitched by hand - many years ago when my eldest son Ben went to South Africa on a rugby tour.