The p2tog and p3tog are used to reduce the overall number of stitches on the needles.

If we couldn't decrease stitches then we wouldn't have the freedom to create any knitting shape we want. Decreases (and increases) are required to add shape to your knitting.

P2tog = purl two stitches together.

This is a single decrease so reduces the overall number of stitches on your needles by 1.

It is the purl equivalent of the k2tog; the k2tog is used on a knit row, and the p2tog is used on a purl row.

P3tog = purl three stitches together.

This is a double decrease so reduces the overall number of stitches on your needles by 2.

It is the purl equivalent of the k3tog; the k3tog is used on a knit row, and the p3tog is used on a purl row.

Both are right leaning decreases, so when viewed from the front of your knitting, they will lean a little to the right. I'll explain more about it in another lesson.

Here is the video tutorial: