What are the two numbers the binary system uses?

In theory any two symbols would do, but usually they are 1 and 0.

So, for example, the binary for three is 11, and for thirteen the binary is 1101.

To make conversions, use the calculator that comes with a Windows operating system. Set the View to Scientific, make sure the Dec (for decimal) button is selected, and key in a number. Then selected the Bin (binary) button, and the binary equivalent displays.