When two groups of humans who don't share a language come together, they generally try to communicate. Often, the result is a pidgin—a simplified language that combines features of the groups' languages while leaving out the more difficult parts, allowing the groups to speak to each other. This sort of lingua franca is often used to conduct trade. (The word "pidgin" comes from an English/Chinese pidgin, where it began as an alteration of the English word "business.")
Although the grammar of a pidgin is simpler than the grammars of its parent languages, and although pidgins often sound like uneducated fumbling attempts to speak one of the parent languages, pidgins aren't just "corruptions" of parent languages; they have grammar and vocabulary all their own. However, pidgins are created languages; nobody is a native speaker of a pidgin.
When children grow up speaking a pidgin, though, they expand the language. The grammar becomes more complex; the vocabulary grows, and words acquire new meanings. This process results in a creole, a natural language derived from a pidgin. (The word "creole" apparently derives from Portuguese "crioulo," a word I've seen defined both as "a European born in the American colonies" and as "a house slave"...) English itself, of course, is a hybrid language drawing on a mix of dozens of languages, but English is not a creole as such.
It's easy to make the mistake of thinking a creole is a "primitive" language or a corruption of English because so many of the words sound or look similar to related English words. But even words that appear to be entirely English may have meanings that don't exist in English, and their roles in sentences may be opaque to those who don't know the details of the creole's grammar. For instance, according to The Story of English, in Melanesian Pidgin (which I think is the same as Tok Pisin), "Fire i-cookim abus" means "The fire cooks the meat"; the -im suffix means that the next word is the direct object (so "Abus i-cook" means "The meat cooks").
The impression that a creole is nothing but "broken English" partly derives from choice of spellings; I suspect (but don't know for sure) that as with transliteration of Chinese, new spellings have come into style deemphasizing Englishness and emphasizing pronunciation. (Some older written works about Tok Pisin, such as Margaret Mead's book Talk Boy, apparently do Anglicize the spellings). For instance, I suspect that the "-im" suffix mentioned above would once have been spelled "him," and originally derives from the English word "him" (though again I don't know for sure).
Pierre brought Tok Pisin to my attention a while back, in discussion of pronouns. Tok Pisin is a national language of Papua New Guinea (one of over 800 languages spoken there!); it's even spoken in Parliament there. It derives from a combination of European (English, German, Latin) and Malayo-Polynesian languages.
Pierre provides a sample sentence in three languages:
- English: I will go to town to buy some lemons.
- Gahuku (a.k.a. Alekano), another PNG language (or possibly Asaro'o): Muli mako alitove loko taoni loka vitove.
- Literally: Lemon some buy-will-I saying town to go-will-I. (The word order is completely backward from English.)
- Tok Pisin: Bai mi go long taun bilong baim sampela muli.
- Literally: Will I go to town for buy some lemon. (Baim is bai+im; the two bai's are unrelated.)
Note that a creole doesn't have to have anything to do with English. The Ethnologue lists 66 creoles, of which only a third are English-based.