Chain stitch is the foundation stitch for everything you create using a straight edge with crochet.
It is like casting on in knitting.
One of the differences between crochet & knitting is that every stitch you do in crochet is like casting off, you only ever have one live stitch.
Whereas, knitting may have hundreds of stitches open if you are making something large.
With crochet, even if you are making a blanket - you still only have one live stitch. The beauty of this is that you can pick up or put down your work at any time. When I’m knitting I tend to finish the row first.