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. In some cases, the pattern might not call for a stitch marker, but you'll choose to use it anyway to keep track of where you are in a pattern.
Using a Stitch Marker
Stitch markers are often used in spots that could be tricky to find later, especially when working in the round. 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. This would create a spiral instead of a circle and could significantly alter the final design of your item.
It is also helpful to use crochet stitch markers when you are working with yarns that have very little stitch definition. For example, if you are working with mohair or another fuzzy yarn, you might choose to use stitch markers to remind yourself of where the next stitch in a pattern should go.
Finally, people sometimes use stitch markers to mark the beginning/end of a pattern repeat. This is ideal for long patterns where there are repeats that you can easily lose count of if you are not paying attention.
Patterns That Call for Place Markers
You can use a stitch marker any time that you feel it is necessary for your work. Some patterns will indicate that a place marker is needed (often using the abbreviation PM). Here are examples of such patterns to give you an idea of what to look for and what types of patterns might call for the use of stitch markers:
- Scrap Yarn Crochet Shawl: This crochet tutorial asks you to work into the center two stitches of a row and suggests using place markers to mark out those spots so you don't get confused as you are crocheting.
- Crochet Baby Sweater Pattern: This crochet pattern uses stitch markers to denote the sleeve openings during the assembly portion of the project.