The processor determines the rate at which data is moved from point A to point B while being rearranged to meet the visual target. An example is changing the 0s and 1s stored in the memory into a song and the album cover you see. The data moves at different rates while it is happening. But say you are watching a HD movie. There are going to be times that the processor might get bogged down due to the demands of the video. What RAM does is when the processor is not busy, it allows the video to get ahead of itself, so that you have less interruptions.
True multitasking is when something is continueing in the background while you work on something else. Again the video analogy. If you were watching a video on the web and switched to another program for a few minutes, under iOS, the video would freeze at the point you switched over, and resume when you switched back. Under true multitasking, the video would continue to play the entire time.
These are just rough examples and it gets a little more complex in reality. for example, you can play music while surfing the web, and other items that are a combination of both. It all has to do with dealing with managing what the processor does when, so that everything runs smooth and effortless for the user. With true multitasking, they either have to have a very good OS to manage the assignment of data to the processor, or they have to over power the process.
If you ever go skiing in the winter, think about how they manage the lift lines when busy. It is the same basic operation. The skiers are data, the lift operators are the OS, and the lift is the processor. If you have eight lines waiting, they will fill all the chairs from several lines at once, but the skiers have to wait their turn according to the priority establish by the operator. When there is only one line, the first in line get seated first. One way to speed up a one line operation would be to go from two seats to four seats. That would be the equivalent of going from a single core to a duo core.