RAM / Memory – Think of RAM as the same as your ability to do math in your head. When you run out of space in your head, you have to start writing numbers down, which is much slower. The same thing happens with RAM but instead of writing it to paper, it writes the numbers to the hard drive which is much slower than RAM. In other words, the more RAM you have, the more and bigger programs you can have running at the same time.
4GB is the minimum for modern systems. We recommend at least 8GB.