Chain stitches / turning chains / beginning chains

Dear users and authors,
could you please explain again for beginners how chain stitches / beginning chains / turning chains work?

Chain stitches are needed to start a crochet project.
Single crochets, double crochets, and all the other stitches are worked into the chain stitches.
Turning chains are used as a substitute for the first stitch (single crochet, etc.).
Turning chains are the same—except that they are worked at the end of the project.

Yes, you need them when crocheting in rows so you can move up to the next row. If you’re crocheting in the round, you don’t need them—you simply work in a spiral without any steps.

@veronika-t15
That’s not entirely correct, because not every piece crocheted in rounds is automatically worked in spiral rounds! When crocheting clothing, you tend to work in closed rounds; to do this, at the end of a round, you make a slip stitch into the top chain stitch of the previous round and then work the new chain stitches on top of that. Often, you also turn the work after each round so that the “seam” doesn’t shift and everything stays in a straight line.