Hi, you are correct, the i3, i5, i7 thing is a processor (CPU). There are many different kinds but two main manufacturers...AMD and Intel. I happen to have an i5 6600k.
The game has required and recommended specs. From my experience (and others here may agree) you should have equipment that meets, if not exceeds, the recommended specs.
RAM is short for Random Access Memory. They are available in "sticks" of various speeds and types. If you think of your computers hard drive as its permanent memory that stores things like photos, games, and other files that are always there when you turn it on...
...then think of RAM as temporary memory that is used only while the computer is turned on. The current types of memory being used are typically called DDR3 or DDR4. RAM is lightning fast when compared to a hard drive and it works in conjunction with the processor and other components.