all that glitters is not gold?????????

It just means that everything that looks good isn´t necessarily the best. For example, you might be offered a job where the pay is very high, so you jump into it, only to find out that you will never see your family because of the hours and you are expected to sleep with your boss, etc. The "gold" turns out to be fool´s gold.

The statement means to beware of phony imitations that might look real but are in actuality, worth nothing. In the case of gold, there is another rock which is nicknamed "Fool's Gold" because it looks just like gold. In the case of people, it means that someone who you many think is a terrific friend is actually someone who is trying to scam you out of something. You should never judge something by the way it looks. There is an old saying "Never judge a book by its cover" which I think is extremely apt here.

The statement is quite right. It is meant to state that we should not judge something's value simply because is it "shiny".