Since these guys are telling you what to do to get answers, I'll tell you some answers. Don't ever think you have mastered knowledge on PCs, because you never will as there is endless things to learn. Don't assume things with computers, 99% of the time you'll be wrong. If there is an issue with software, it won't magically fix (Unless there is an automatic bugfix, but you should know that much). Research the error and find the solution.
SSD vs HDD: SSDs are what you want to have your frequently played games on and your operating system. SSDs are much faster than HDDs, its just HDDs are very affordable and can store whatever you so desire.
When looking for a CPU, compare them using CPUboss and benchmarks. Don't be biased when picking either Intel or AMD processors, go with which one is better and affordable in your budgets. You typically want to have a high core, high clock, and high L3 cache with a lot of threads.
With videocards, the more ram the better, the more clock speed the better, and the more CUDA cores the better. Get something that supports the newest versions of Direct X. Again, don't be biased between Nvidia and Radeon video cards, go with the better and more affordable one. Be sure to buy one with proper cooling to it, or it will quite literally set fire, smoke, and or Melt down. With Crossfire and SLI, you will need a lot of PSU power and support from the motherboard. Crossfire and SLI are fancy terms for Multiple video-card usage on the same motherboard.
With RAM, you want the highest clock speed. DDR4 > DDR3 > DDR2 > SDRAM. Don't think about getting DDR2 or below. DDR4 right now is absolutely amazing, but only Intel processors support it. AMD is releasing a new line of CPU called the Zen series, which will support it. Good RAM companies, Crucial, GSKILL, and Corsair
Power Supply Units, or PSUs as most call 'em give your computer the power it needs to run. You want to get a power supply that is gold or platinum certified. The more wattage on a powersupply, the more power it draws and disperses. Power supplies are pretty straight forward. You want to get enough power to the videocard(s) and CPUs
With a case, try to just look on this forum for the best cases right now and the best cooling systems to put in place. Don't forget to use thermal paste when connecting your cooling system to your CPU. You will be able to fry an egg on the CPU if you don't. Go for a case that is mostly steel, because plastic cases are just cheap and will not do you well. Now-a-days, you want to get Liquid cooling for the CPUs, as it is reliable. Liquid cooling is also a pain to setup, but worth it. If you don't want the pain of setting it up, but want the liquid cooling, buy a case with liquid cooling preinstalled. DEEPCOOL Genome, awesome case.
Motherboards can be tricky too. Research the best motherboard to pair with the CPU you so desire, because motherboards are damn annoying if you don't know what to do with them. Motherboards have CPU sockets, of course, but some CPUs fit in different CPU sockets, so of course you have to get a motherboard for a certain line of CPUs. For amazing builds, find motherboards with a lot of RAM slots(8x), or just go with 4 slots for more subtle and non-Megatron builds. Motherboards will have tons of stuff on them when you get one and you will not understand a single bit of them. You'll have to read the manual to know where to begin.
Use PCpartpicker and tech support from newegg.com to find what you want and what goes well with each other. Also, shop at newegg.com it's amazing for prices, customer support, good deals, and overall quality and availability. Don't thing you're an expert after reading this. This is just a guide for a noobie as if someone who is legit an expert would look at this and cringe.