The video demonstrates how to do the two stitches used to make the raspberry stitch, which are purl 3 stitches together, and knit 1 purl 1 knit 1 in the same stitch.
To purl 3 stitches together, simply take the next three stitches on the left needle at the same time and purl them together as if they were one stitch. You are basically taking 3 stitches and making them into one stitch.
The knit 1 purl 1 knit 1 in the same stitch is done as follows: knit one stitch as you normally would but don't slide it off the needle; move the yarn to the front of the work and purl one, again without sliding it off; finally move the yarn to the back, knit one stitch and slide it off the needle.
These two simple stitches create the very attractive raspberry pattern.