Something provisional is not final. It is good enough for now, but people expect it to change. A provisional government, a provisional timetable, a provisional licence — all of these are temporary, “until we know more” or “until the real one is ready.” It is a formal, official-sounding word. In everyday speech, people often just say temporary. Though actually, it does not mean “probably wrong.” It means “we have not locked it in yet.” As a noun, a provisional can mean a temporary version of something (for example an extra stamp issued for a short time). In older British and Irish news, the Provisionals was also a name for one political group; that is a special, capital-letter use, not the learner’s everyday adjective. The sense you need first is the simple one: agreed for now, open to change.