The outter Camo gear is just part of the solution. You can use the same jacket if the weather is not extreme, hot vs cold. The same jacket may work in 40 degrees or 60 degrees. You can add a wool shirt, knit, fleece, or vest. Be sure to check out the link at the end for ideas.
It depends on what you have, but the base layer that I use is either light, medium or heavy depending on the weather and made of polyester, blend, merino, or heavier wool. Silk is also a base layer. It needs to breath, and move moisture to the outside, keeping you dry. Avoid cotton, unless it is warm and breezy. Forget cotton in hot or humid climates.
The base layer is followed by light, medium or heavier weight socks, pants, shirt, in similar materials. I try to avoid cotton, because it retains moisture, doesn't breath or dry out.
I might stop at the second layer in milder weather (camo shirt, or light jacket) and add the third layer in cooler or cold weather. The outer layer is usually the camo, wool or something for rain. It may depend on what I am hunting and how much sitting or walking is involved. Layering allows you to add or remove something to stay comfortable.
If you go to a specialty store, or Cabela's you will see clothing for layering. It does not have to be expensive, because some surplus stores may have what you are looking for.
There is a lot you can find online,
http://www.basspro.com/webapp/wcs/stores/servlet/CFPage?mode=article&objectID=29900&storeId=10151&catalogId=10001&langId=-1