A gezel is a journeyman, a craftsman who had already finished basic training but had not passed his master’s exam yet and had not been admitted to the guild. The term is also used to indicate someone who worked for a boss rather than having their own shop, so a gezel doesn’t mean the person is young.
You can find the word gezel used as a suffix to other occupations, for example a timmermansgezel (journeyman carpenter) or schoenmakersgezel (journeyman shoemaker). You won’t find these composite terms in most dictionaries, so just look up the first part (without the -sgezel) to see the craftsman they were apprenticed to.