What are the differences between formal and informal English?

Written english. In all english speaking countries is the same.Some slight differences in spelling english colour labour sulphur americans spell the same words color labor sulfur makes no difference to the spoken language The oxford dictionary has over 500,000 words Formal english takes no account of dialects accents slang etc Informal english is the idiom a specific area used by the local inhabitants.However that local idiom is written in proper english

The closest equivalent of tu/usted in English would be using someone's first name as opposed to their last name. So if someone was called John Smith, then formal would be Mr Smith, and informal would be John. However note that over the last 50 years it has become much more common to use someone's first name in English-speaking countries, particularly the US. So you might well use first names with people that you wouldn't use tu with in Spanish. "Sir" and "Madam" are formal but are only used when you are deferring to someone (that is, you are treating them in a more respectful way than they should treat you, like a waiter would treat a customer).

informal is the colloquial or conversational form. otherwise it is formal

I ain't exactly sure there, friend.

I must claim I do not know.