You can write numbers in other bases. Computers usually report their answers in base ten, but they do the computations in base two. You can think about binary counting in a couple ways. Imagine an odometer with only 1's and 0's, so instead of advancing when the rightmost digit goes from 9 to 0, the second digit from the right advances when the rightmost digit goes from 1 to 0. Or, you can just write down all the decimal numbers that only use 0's and 1's, in order.
Exercise Try counting higher.
Let's try another example. Exercises Turn the following binary numbers into decimal numbers. This is a little harder, but not too bad. Suppose you want to change 23 into binary. Exercises Turn these decimal numbers into binary.