Let's think carefully about our usual base-10 (decimal) notation.
When we write 2095, we mean 2 * 1000 + 0 * 100 + 9 * 10 + 5 * 1.
Or, if we like using exponents, 2095 = 2 * 10³ + 0 * 10² + 9 * 10¹ + 5 * 10⁰.
Note that each digit in the sum is a number between zero and nine; there is no need for symbols greater than 9, because ten times 10^k is reckoned for by adding one to the 10^k+1 place.
Binary representation works on the same principle, except that each place now represents a power of 2, i.e., 2^k.
So the binary number 1101 represents 1*2³+1*2²+0*2¹+1*2⁰=8+4+0+1=13.
Note that we only need digits 0 and 1 for binary representation (just as we only needed digits 0 to 9 in decimal representation), because two times 2^k is reckoned for by adding one to the 2^k+1 place.

Practice
Conversion from Binary to Decimals