what is the difference between british english and american english?

Capitalize the first letter of all sentences.

This is an incredibly broad question, which no single response can adequately cover. British and American English sometimes diverge in spelling, usage frequency, word meanings, current and obsolete definitions, pronunciation, colloquialisms, slang, idioms, neologisms, dialect, jargon and punctuation. Consequently, no post will neatly break down the difference specifically.