As a science teacher, modeling and making analogies has proved to be helpful to students. I would have students create models and analogies for the different hardware components of the computer.
The following is an example of what I might be expecting:
A computer is like a kitchen at a restaurant.
The computer's processor is like a chef, who works to prepare the food. The faster the chef, the faster food is ready. A dual-core processor is like having a kitchen with two chefs, so two things can be prepared at the same time.
The computer's RAM is like counter-top space. Everything in RAM is easy for the processor to get at, so if you have a lot of counter space, the chef can work on preparing more things at once. If you don't have enough counter space, the chef can't work on as many things. Some programs use a lot of RAM, just like some recipes call for a lot of ingredients, so it is harder to fit more stuff on the counter.
The computer's hard drive is like the cupboards and refrigerator. These things hold the ingredients until the chef needs them. If space runs out, then the old ingredients need to be thrown out to make room for new ones.
You, the computer user, are then the customer who is ordering things from the kitchen. If the chef is slow, or their isn't enough counter-top space, it's going to longer for things to get done, especially if you are ordering a lot of things at once.