They are all a bit of a jumble if I'm honest. Especially that first one that tells you to use the power supply the case includes, it should be basic knowledge that these are generally terrible.
As far as quality on parts, brand is important, For motherboards I only look at Gigabyte or ASUS and for power supplies I only tend to look at the likes of XFX, Corsair (Non CX/VS series), Antec, SuperFlower, Seasonic.etc. The brand of RAM isn't that important though and if budgets are really tight you could always get a cheap case, although they can be noisy and a right pain to build in.
The key thing to remember is to stick with quality, even the most basic Celeron based office PC I build will still get a Gigabyte/ASUS board and a good power supply (Usually Seasonic OEM ones at that level). It's a bad idea to compromise on quality just to save a bit of money, it'll likely cost more in the long run.
Gaming PCs are not cheap, when you start trying to cut corners you will have trouble. You get what you pay for.
