This is called your setting
Setting is a very real part of any book, and especially of fantasy novels, as they take place in an unfamiliar setting, and therefore require more explanation. Setting is more than merely the backdrop for the story though. Through its rules, you can create circumstances you normally couldn't (ie, magic and the like), often driving the plot forwards. Its most powerful use though, is creating mood. If you're writing a cheery novel, you probably won't set it during a dreary rainy day. Likewise, if you are writing a horror tale, odds are it doesn't take place in a summer valley at high noon. Those are of course basic examples; you can use setting to convey mood in a much more detailed manner, as well as use it to show parts of your characters. However, that was not your question.
When it comes to setting in novels, there is one very simple rule: Do not infodump. Infodumping is when an author, having a surplus of information which might or might not be relevant to the actual story, decides to dump it all in one place. The reader is correspondingly overwhelmed, and usually driven away by the lack of story. Remember, the reader is reading for the story, not the setting. Stop the story and you lose the reader.
So where do you put your setting? Everywhere.
Show your setting through your characters. Don't focus on it. Have your characters interact with it naturally, in a normal fashion. Let the reader draw his own picture of what they are seeing, touching, smelling, or hearing.
Show your setting through the emotions. If your characters feel a certain way, have that reflected in the setting. Once again, don't focus on it during the description, merely mention the clouds, the sun, the grass, the man-eating trees - whatever there is - as you go along.
Show your setting through the plot of the story. Maybe that man-eating tree is a major plot device. Are the social habits of the orcs a main part of the plot that has to be described? Are you sure? Really? Okay then, have one of your characters discover them as the plot goes. You say all of your character know the social habits of orcs? Create one that doesn't. If it comes to it, have him ask questions that the others answer.
You can see the common thread here. Show your setting through your story as your characters come across it. Don't force the description. Let it flow naturally. Never focus on it, unless it is actually a part of the plot. And if it is, check again. Ask yourself if the reader really truly needs to know this about your world.
That will be the hardest part: realizing that a lot of your setting won't be in the novel because the reader simply doesn't need it. As @what said recently on a different question, you can take that extra setting and put it on your site. By all means include it in an appendix (keep it in the back, otherwise the reader might start with it and become bored). Include a glossary, especially if there is a complex net of characters and places to remember.
The basic rule is this: Don't tell your setting. Show it through your story and your characters naturally.