The Twill Stitch is worked by bring the needle up at the top left (1) across three threads in the canvas and down (2). Bring the needle up again to the lower right of the bottom of the stitch you just made and repeat, working a diagonal row.
The next row (shown in a slightly lighter color for clarity) is worked in the opposite direction
Repeat to fill the desired area.
If you would like to add this stitch to your stitch journal, see step 3.