"Il est cuisinier."
Translation:He is a cook.
A chef and a cook are actually not the same thing in English:
A chef, short for "Chef de cuisine" (which is where chef originally came from), is the chief of cooks, working in a restaurant with several people working underneath him (including cooks).
A cook is simply someone who prepares food.
In French, when saying that someone is a profession, an article is not used. It's used like an adjective rather than a noun. If you wanted to use it as a noun to stress that they are a SPECIFIC cook, you would use "C'est" instead of "Il est." For example, "C'est ce cuisiner" means "He is that cook."
In French, "chef" means head, leader, boss, chief (i.e. the one in charge). The chef in the kitchen is in charge of the kitchen. "Chef" is also used as chef de chirurgie (chief of surgery), chef de délégation. (head of the delegation), or le chef de l'opposition (leader of the opposition). Here's a link for "chef" in context. (http://context.reverso.net/translation/french-english/chef) "Cuisinier" is someone who cooks.
The statement translates to He is a cook. You do not need an article if using il est. You could also use C'est un cuisinier to say the same thing. If you use C'est, you need an article. If you use Il est, you don't. I think the notes to one of the lessons tell you about this.
Also see here: http://french.about.com/library/weekly/aa032500.htm