This cable is worked across 4 knit stitches, crossing 2 knit stitches with 2 purl stitches.
To create a cable that slopes to the left you slip the first 2 stitches onto a cable needle and hold that needle at the front of your work. Now you purl the next 2 stitches. Finally you come back to the 2 stitches on your cable needle and you knit them.
This is called a 2/2 LPC which means that 2 stitches cross with 2 stitches forming a Left Purl Cross.
Here is a video of this at work:
This is what this stitch looks like when it’s shown in a cable chart. To break down how the stitch is worked you can use this illustration: