Leave it on the crochet hook and tug gently on both ends of yarn to tighten it up. Don’t over-tighten it; the crochet hook should be able to move easily inside this loop so that you can form your starting chain in the next step.
Next: After the first slip knot has been made, most crochet patterns start with a foundation chain.
Tip: Note that, in crochet, the beginning slip knot or slip loop is not usually counted as a stitch. This differs from knitting, where the first slip knot does create a stitch.