These two varieties of English are very similar that most American and British speakers can understand each other without great difficulty.There are,however,a few differences vocabulary and spelling.
Some words only exist in one form of English,whereas others may exist in both,but contain completely different meanings.For example,Elevator and Lift.Gas/Gasoline and Petrol.
Many words are also spelled differently in American and British English.For example,British words that end in -our (colour,flavour and humour) end in -or in American English (color,flavor & humor)