@indemnifyme - The plasma membrane was one of my favorites in biology too. Once you learn about the plasma membrane, a lot of other stuff about the cell is easy to understand.
For example, once you've got the idea of membrane proteins down, passive and active transport are easy to understand. Also, as you pointed out, there are membranes inside the cell too. Once you understand the plasma membrane around the cell, the interior membranes make sense too!