The LEN function is fully automatic. In the example, the formula in the active cell is:
The LEN function simply counts all characters that appear in a cell. All characters are counted, including space characters, as you can see in cell C9.
Numbers in Excel (including dates, times, currency, etc.) are often formatted with a number format. It's important to understand that the characters that make up numbers are counted in their raw form (i.e. number formatting is not included). For example, because Excel dates are serial numbers, the result in cell C11 is 5, since the date in B11 is is actually the number 42005.