The chain stitch is used for many purposes in crochet. Often it is used as a basis to start of with your crochet project. When you crochet rows, you will start a new row with one starting chain or more.
The symbol in charts that is used to indicate a chain stitch is an oval like the one you see left. As abbreviation is used ch.
Chain stitch video-tutorial
Crochet the chain stitch step by step
Step 1: Start with a movable slip knot. Make sure to have a bit of tension on both threads. To hold the tension on the long yarn end, you can guide the thread over your index finger and hold it between your index finger and middle finger. Hold the short yarn end between your thumb and index finger.
Step 2: Wrap the thread around the crochet hook like in the image one time (this is often indicated in patterns as ‘yarn over’). Now pull the yarn through the loop that is on your crochet hook.
Step 3: Pull the yarn tight enough that it is snug on your hook. But not too tight, because that will make it difficult to work the next row. Now you have finished your first chain stitch! You can repeat this to make a foundation chain.
It is good to know how to count the stitches you have made. I have made 6 chains in the image above. I pointed every stitch out with an arrow. You will crochet (for example) a next row into one of the indicated stitches.
Do you want to learn more stitches? You can find an overview of the stitches HERE.