The pattern uses US crochet terminology. The stitches and abbreviations used in this pattern are:
Ch – Chain
Sc – Single crochet
Hdc – Half double crochet
Dc – Double crochet
Tr – Treble crochet
Sl st – Slip stitch
St(s) - Stitch(es)
Chsp – Chain space (ch2sp = chain space with 2 chains, ch4sp = chain space with 4 chains etc)