Basically the digits are arranged in any number such that every position has its unique “place value”. When you obtain the products for each of its constituent digits with its corresponding place value and add them up, you get the number. Below are a few examples.

\begin{align}

  & \text{eight}={{10}^{0}}\times 8 \\ 

 & =1\times 8 \\ 

 & =8 \\ 

 & \text{eighteen}={{10}^{1}}\times 1+{{10}^{0}}\times 8 \\ 

 & =10\times 1+1\times 8 \\ 

 & =18 \\ 

 & \text{one hundred and eight}={{10}^{2}}\times 1+{{10}^{1}}\times 8+{{10}^{0}}\times 0 \\ 

 & =100\times 1+10\times 8+1\times 0 \\ 

 & =180  

\end{align}\