The most succinct way to convey most knitting patterns is as a chart. This Demonstration incorporates symbols for many basic knitting stitches, letting you build charts by placing different symbols on the grid. The easiest way to save a completed chart as an image is to take a screen shot and crop it so that only the chart is shown. Symbols that span multiple stitches are added with the leftmost square being the one clicked. This is why, on Snapshot 3, the "delete" X is only needed to be placed over the leftmost square.
Snapshot 1: charts can be scaled to match the size of the repeat, and there are options for both 1×1 and 2×2 cables
Snapshot 2: adding a purl and then a decrease or YO on the same square allows for purled decreases or YOs on the purl side
Snapshot 3: the purl symbol can also be used for colorwork patterns; also, the "delete" button removes all symbols beginning on squares marked with the red X