Stitch markers are essential tools to crocheters and knitters alike. They can be used to mark a certain number of stitches, the beginning of a round, where to make a particular stitch, and more. Patterns often call for stitch markers with the abbreviations "pm" (place marker) and "sm" (slip marker). It's important to note that there are essentially two categories of stitch markers: closed and open (also known as split-ring).
As the name implies, closed stitch markers feature one solid loop. They come in a wide variety of styles, including simple plastic rings and more complex charms. Here are a few examples:
While knitting, the stitch marker sits on the needle between active stitches. To start using a closed marker, simply knit to where you want the marker, then place it on your right needle. Continue to knit as normal. Keep in mind that the marker can only be adjusted when you reach it in the row. When you reach the marker, simply slip it from the left needle to the right (as you would slip a stitch) to keep the marker in the same position.
Closed stitch markers do not work with most crocheting techniques. This is because crocheting closes stitches instead of leaving them live. Thus, if you used a closed stitch marker, it would be crocheted into your work. The only ways to remove the marker would be to rip out your stitches or cut your work (yikes!).
Open or split-ring markers are incredibly versatile. Because they aren't closed, they can be added, removed, or adjusted at any time, regardless of which stitch you're on. They come in a variety of different styles, including rings with a small gap, locking, or lever-backed.
When knitting, these markers can be used on the needle (as with closed markers) or attached to particular stitches.
Because they can be removed at any time, open stitch markers are perfect for attaching to crochet stitches.
Those are the basics to selecting and using stitch markers! If you find yourself in a pinch and don't have a stitch marker handy, try using a tie of yarn (for closed stitch markers) or a paperclip (for open stitch markers).