Early Decision II is BINDING (just like ED I is), it just has later deadlines. It essentially lets someone who has not gotten into their first choice ED school take another shot at the ED process at a different school. You MUST withdraw all other applications and attend the school if you are accepted ED II (just as with ED I). Early Action is typically non-binding, but gives you an earlier response to whether you are accepted or not (or you can be deferred into the regular decision pool as well).
Read the information on each school's website carefully to understand their definitions, but those are the standard definitions for those terms.