The binary system that computers use to store and process information is a base 2 system. It needs only two symbols, 0 and 1. In fact, "binary" comes from the Latin word for two. Compare this to the decimal system you use. The decimal system is a base 10 system. ("Decimal" comes from the Latin word for ten.) It has 10 symbols (0, 1, 2, 3, 4, 5, 6, 7, 8, 9).
So how do you count in a binary system? How do you represent numbers like 103?
In decimal (base 10) numbers, you have a 1s place, a 10s place, a 100s place, and so on, to represent value.
The binary system has places or columns too. Only because you're in base 2, instead of each place being 10 times greater than the place before it, each place is only double (2 times) the one before it.