Cables in knitting are formed by crossing stitches, and creating a twist in the fabric. Every cable pattern is basically just a variation on this theme. This tutorial illustrates how to cable by knitting a very basic 6-stitch cable. As you see below, you will be knitting the leftmost 3 stitches first, then the rightmost 3 stitches, and this re-ordering of the stitches will form the cable crossing.
Then you’re done, and since you knit the 6 stitches out of order, you created the twisted in the knitted fabric which forms a cable! Continue knitting as established, and your cable will show more clearly after a few rows. Typically, you will only do this cable cross maneouver every few rows (for a 6-stitch cable, you will do a cable cross every 6th rows, for a 4-stitch cable, you will do a cable cross every 4th row, etc.)
This 6-stitch cable is the cable pattern used in my Chunky Cable Hat – a free pattern.