A website or a handwritten guide would be nice.
I want to build a gaming PC

Some questions I have:

I have this old crappy PC that is about 7 years old, could I just take that apart and replace the graphics card/motherboard/processor?

Would this save me more money instead of buying a PC? About how much would I save if I do?

What else would I need to upgrade besides a graphics card/motherboard/processor? The power supply and fan?

Is newegg the best site to buy computer parts?

Is it fairly easy to build a computer? In other words, can a non-idiotic 16 year old do it?

Also, let's say I'm looking at this graphics card, where do I find out what kind of motherboard I need? I see the power requirement is 400W+, but I dont see anything about a motherboard. Or is it the motherboard that explains that kind of graphics cards it can hold?

Also if you want to suggest computer parts for me, it would be nice. I'm noob when it comes to building computers/computer tech, I just like games.
I'm not looking for super high end $400 graphics cards, but somewhere in the $100-200 range for each part would be nice.

And if you want to suggest some pieces, try not to go over $1000. As cheap and as best as possible. $600-$700 would be an ideal range