Romans 1:20 (NKJV)
For since the creation of the world His invisible attributes are clearly seen, being understood by the things that are made, even His eternal power and Godhead, so that they are without excuse
A creator of everything must, by definition, exist outside of his creation. But can you know anything about the creator by examining his creation? Perhaps that can be answered by asking if you know anything about the artist by examining a painting? Certainly you could be impressed with his skill and sense of beauty. By studying a number of paintings, you might even be able to get a little glimpse into his personality. Two things we can know for sure are 1) if there is a painting there must be a painter and 2) the artist is greater than his art.
If God exists then why doesn't he reveal himself to us? He has revealed himself in many ways: through his creation, through fulfilled prophecy, through the bible, and through his dealings with Israel. Most importantly, he has revealed himself by stepping out of eternity and becoming a man identifying with us and becoming our kinsman redeemer. God has revealed himself to us which is why this verse says that we are without excuse.
Job 12:7-9 (NKJV)
But now ask the beasts, and they will teach you; And the birds of the air, and they will tell you; Or speak to the earth, and it will teach you; And the fish of the sea will explain to you. Who among all these does not know That the hand of the Lord has done this?