This pattern is written using standard US crochet terms and it is for one size fits most adult women.

Central single crochet (waistcoat stitch) tutorial - https://www.youtube.com/watch?v=cdSfYr5Su0g

Ch 1 throughout the pattern doesn’t count as a stitch.

Increase stitch is completed by doing 2 central single crochets into the middle of single crochet.

Decrease stitch is completed by pulling up a loop in the centre part of the next 2 single crochets and pulled through all 3 loops.