The Stem and Outline stitches are often background stitches in smocking. Simple to do, they don't often take center stage, but instead are usually used to complement other smocking stitches. The two stitches are mirror images of each other, and the difference between the two stitches is solely whether the thread is kept above or below the needle.
Bring the thread to the front and get into starting position. (See this tutorial that explains how to start.)
Move one pleat to the right (or left if you are left-handed), and take a stitch, keeping the thread always below the needle for the stem stitch.
The needle always remains parallel to the pleating threads as the stitch is taken. The slight slant that the stitch forms is due to the next stitch pushing the previous stitch out of the way.
the outline stitch is formed in the exact same way except the thread is always kept above the needle.
Here is the finished outline stitch.
The thread often gets twisted in stitching both outline and stem stitches, so stop often, take the eye of the needle down to the fabric, and straighten out the thread.
The wheat stitch is a combination of the stem and outline stitches butted up next to each other, and it is here that outline and stem get to shine. I find it easiest to stitch the bottom stem stitch first and then stitch the outline stitch right next to it.
The base fabric should show in the middle. Here is the finished Wheat Stitch.