Yep you do exactly like it says, lift the yarn that's between the sts and purl into it. There's a video for the knit version, which is somewhat the same, you just purl into it instead of knit. There's also a video for ptbl on the Glossary page, but it may be easier if you lift the yarn with the needle from back to front then purl through the front loop. What you're doing is twisting the st so it won't make a hole. If you want, you can pfb instead, but you have to do that in the stitch before it says to m1p.