What do we call a cover of a choclate or candy bar? there is a paper or plastic which covers things like candy, chewing gum, and this kind of food stuff.

Longman Dictionary suggests foil? Is it the word used in everyday English?

Aluminium foil perhaps?
The most general word is "wrapper." You take off the wrapper in order to eat the candy. (You can also say "unwrap the candy.") The wrapper might or might not be made of foil.