We know now what kind of stuff the computer works with. Now we are thinking what the computer does with the information. Mainly, information just sits there doing very little. The information sits in a series of switches who just hold things. This type of switches is referred to as memory. Memory just holds things. You can get stuff from memory, and put it there. You can't really change anything directly in memory.
You might think of memory as a whole bunch of tiny mailboxes. Each mailbox has an address and contents. If you want to put something in a mailbox, you need to know the mailbox address and the contents to put in it. Most of the time as a computer user, this process is hidden from you, but you ought to know it is happening. Each mailbox can only hold very specific amounts of information. For example, if you are typing a letter using some kind of word processing program, each address of memory might contain one character. Since you know that computers can hold long documents, you can see that there are many such addresses in a typical computer, and they could be difficult to deal with, but your word processing program will handle it for you. You don't have to deal directly with all these addresses.
Memory is good for storing things, but computers do more than simply storing information. They need to be able to do things to information. Computers use special place in memory to hold values while they work on them. These special places are called registers. You can think of registers as "information garages". Think of taking your car to the body shop. When you take your car in to have some work done, they usually do not take it directly to the service bay. Instead, they put it in a parking space. When the mechanic comes in, he might be told "Fix the bumper on the car in space 32." He does not go out to space 32 to do all the work, because it might be cold out, and all his tools are in the service bay. It makes much more sense to bring the car into the garage and work on it there. Then when the work is done, he might take it back out to space 32. Registers work in pretty much the same way. If you tell a computer to do something to a number in memory, it will go to the memory address, copy the value of that address to a register, and do whatever you want to the value now in the register. It might then copy the value from the register back to the memory area.