Here is an example of converting the binary number 01010101 into decimal. Each digit is equal to a power of 2 (from right to left, 1, 2, 4, 8, 16, etc). If the digit is a 0, then we have 0 * power of two = 0, if the digit is a 1, we have 1 * power of two = power of two, for instance here 1 * 1 = 1 for the rightmost column and 0 * 2 = 0 for the next column. This animation steps us through a conversion. This example comes from figure 3.1 in the textbook.