ssp        Slip Slip Purl
             Slide the first stitch on your left needle knitwise to the right needle. Same for second stitch on the left. Slide both back to the left needle
             (you made a twist in the loop)
             Insert right needle through the back loops from left to right on both stitches (second stitch goes first this way)
             Purl both stitches. Decrease of one stitch.

Step 1:
Slide the first stitch on your left needle knitwise to the right needle.

Step 2:
Also slide the second stitch on your left needle knitwise to the right needle.

Step 3:
Slide both back to the left needle (you made a twist in the loop)

Step 4:
Insert right needle through the back loops from left to right on both stitches (second stitch goes first this way)
Purl both stitches.

Step 5:
Decrease of one stitch.