An accumulator machine is like a piggy bank that counts coins. When you put coins in the piggy bank, it adds up how much money you have. The accumulator machine is like a piggy bank for a computer. It keeps track of different numbers while you use a program.
Let's say you want to add two numbers together on a calculator. The accumulator machine would "hold" the first number you enter, and then when you enter the second number, it adds them together and stores the answer. This is how the calculator can show you the sum of the two numbers you entered.
In more complex programs, the accumulator machine keeps track of lots of different numbers and performs lots of calculations. But the idea is the same – just like a piggy bank counts coins, the accumulator machine counts and calculates numbers for the computer.