What decreases are there in Knitting?
Decreases remove stitches, narrowing the knitting. The most common ones you will find in patterns are K2tog (knit two together) and SSK (slip, slip, knit). They’re easy, just watch the videos. There are also double decreases, which remove two stitches at once. I don’t feature any of these on that decrease page, but you’ll find at least one in the Glossary (see, for example, CDD).”
At Unravel & Unwind we used these tutorials as back up resources in between our knit-a-long classes. Here’s a short video that has a good visual representation of 2 methods described in the link above.