Single crochet (US terms) is the shortest, most basic crochet stitch: insert the hook, yarn over and pull up a loop, then yarn over and pull through both loops. It makes a dense, sturdy fabric ideal for amigurumi and washcloths.
In UK terminology this same stitch is confusingly called 'double crochet' — always check whether a pattern uses US or UK terms. Single crochet's tight fabric is why it's the default stitch for stuffed toys.