Its really far too much to go through on here for any of us - all you need is some practice, take apart old machines and have a look, don't worry about what you may do, and try to put it back together afterwards. When you make that work; you will know enough to build one yourself with real stakes.
Things like Custom PC, some Gaming Magazines and most Computing Magazines will help a lot. Even if not specifically on the process of building - certainly on the Computer side of it, and what sort of things you should do and buy for the best performance and value.
A Knight is sworn to Honour. His heart knows only Virtue. His blade defends the helpless. His might upholds the Weak. His word speaks only truth. His wrath undoes the Wicked.