Wondering what it means when you find the instructions to "place a marker" or "place marker" in a crochet or knitting pattern?
A "marker" refers to anything you could think of to mark a specific spot on your work. The best stitch markers are impermanent and easily removable. Manufactured stitch markers are easy and convenient to use for this purpose. You can also loop, or tie on, a bit of scrap yarn or thread not such an elegant solution, but it does work. If you have a small safety pin handy, it would also make an acceptable stitch marker.
Once you've figured out what you're going to use for your marker, the next step is to attach it to your work in the spot(s) specified in your pattern.
Stitch markers are often used in spots that could be tricky to find later. For example, if you're likely to zone out while you're crocheting, you'll probably want to use them to mark the beginning / ending of rounds so that you don't crochet (or knit) past them without being aware of it.
Pictured above: Clover locking stitch markers, which are designed especially for knitting and crocheting. You can compare prices on these stitch markers at Pricegrabber.
See Also: Knitting stitch markers