If I were a first time builder, I would look at what you're getting for the price. As of right now, AMD's FX line of CPUs are very good for the price. If you're mostly into gaming, then these CPUs will be good for you. They're cheaper and they perform just as well as Intel's i5 CPUs in the vast majority of games up to 60 frames per second. When you start going into 120 frames per second, then you might have some issues. But 120 frames per second can only be done on very high end graphics cards and monitors anyways, something that a first time builder probably won't be messing with. If you get an AMD FX CPU, you want to get one in the 6000 series or higher because those are the ones that will last the longest when it comes to futureproofing your PC for the next year or 2. The 6000 series CPUs have 6 cores. The 8000 series have 8 cores. I have an FX 8350 and I'm able to play every game out there very well. But I also have an R9 280X graphics card.
When building a gaming PC, you want the majority of your money to go to the graphics card, then the CPU. The graphics card is more important than the CPU. But, you need a CPU that will be able to utilize the graphics card nicely, which most of those FX CPUs I mentioned can do. If you spend $300 on a graphics card, then you should spend about $150-$200 on a CPU. This isn't precise math but it's my own math I made up that has worked for me in the past.
edit: Don't worry about individual core performance vs more cores right now. Just look at price for the most part. When you have built a few more PCs then you will be better suited to be able to understand core performance and such.