Weight +, Body Fat Percentage -

[Demonakat]

Go to bodybuilding.com to get your information.
The majority of people that will post and help you are body builders themselves and personal trainers. I've gotten loads of information off of there. It's why I picked the Personal Training cert I'm going for. They have articles you can make and submit and they check those to make sure they're decent. They have scientific studies backing what they say.
Also, Livestrong.com is another one I go to. They also use studies to get their information.
There are more fitness oriented people on the forums there that will correct mistakes and tell someone they're wrong about things. That way you don't have conflicting information based on broscience or misinformation.

Also, leangains works. But it's a combination of proper diet and nutrition and working out. This guy also puts his information based on scientific studies and fact, instead of the "eat 7 times a day to help speed up your metabolism" junk that most people tell you. He busts the myth with scientific fact.

Also, whey protein? this is called Casein protein. Nobody ever mentions Casein, it's like they don't know it exists.

differences and how you should use it.

[Conscious]

Is it possible to gain weight while lowering your body fat percentage, or do these two oppose each other?

I ask because I am sitting at 12% body fat, but as much as I want to gain weight, I also want to lower my body fat, so my muscles become more visible (mainly the ab area).

Muscle weighs more than fat. Thus, you're actually going to get heavier if you're seriously interested in mass and size gains. However your BF% will go down.

That said, generally mass and BF% decrease together as you diet and lose weight without the intent to build muscle. Bulking up and cutting down however, will generally keep a decent looking mass amount (as long as your diet keeps in check) as well as losing that pesky BF%.