A number base is the number of unique digits, including zero, used to represent numbers.
For Ex: Binary System = Base 2 (0,1), Octal System = Base 8 (1-7), Decimal System = Base 10 (1-9)
Any number in base b can be written like this:$$(d_nd_{n-1}\dots d_1d_0.d_{-1}d_{-2}\dots)_b$$
Where: $$(d_i$$ are the digits (each must be less than b)
To convert it to decimal (base 10): Multiply each digit by b raised to its position: $$d_nb^n+d_{n-1}b^{n-1}+\dots+d_1b^1+d_0b^0+d_{-1}b^{-1}+d_{-2}b^{-2}+\dots$$
