Every piece of crochet begins with a slip knot. It serves to secure the yarn to the crochet hook in order to make the first foundation chain. A well-made foundation loop should be stable and not stretch.
In order to make a foundation loop, you need to form a ‘teardrop’ loop from the yarn, crossing the ends in the place where they close, then interweave its free end through the center in such a way so that another loop is created. It is this loop which should be put on the crochet hook. The previous loop should be pushed downwards, thereby securing the yarn to the hook.